Mary headed to Gloucester. When they arrived, the church bell tolled. They drove around, looking for anything conspicuous; a person hiding in a car, a camera or microphone somewhere. When they were assured that no one was monitoring the cathedral's surroundings, Mary parked the car on the parking lot near the entrance which was on the side of the nave. The cathedral was a huge and majestic building with a large tower.

They crossed the square between the parking lot and the entrance. The doors were closed. They looked at each other. Sherlock quickly thought of the best way to get in without causing any disturbance that might inform Walker of their presence. Then he realised that for safety reasons, churches don't lock their doors when they're in service. He tried the door, it opened and they saw an usher in black uniform. He put a finger against his lips. 'I'm sorry but you're quite late,' he whispered. 'I'm afraid the service has already started.'

'I'm so sorry,' Mary said with tears in her eyes. 'We came all the way from London for this service but there was an accident on the A40.'

The usher still looked stern. Sherlock put his foot between the doors and grabbed the usher by the collar, pushing him backwards into the church. The usher immediately fought back.

'Shhh!' Sherlock said in his ear. 'There's a bomb in this church and if we evacuate, we'll probably set it off. Now help us.'

The usher relaxed his grip and stepped back. He'd turned completely white. They were in a hallway that was separate from the actual church. John and Mary entered behind them. Mary had immediately stopped her performance.

'What can we do?' the usher asked with a trembling voice.

'He can probably see us,' Sherlock whispered. 'Is Tom Walker attending the service?'

'We don't keep track of the people who attend Midnight Mass,' the usher said.

'He probably isn't, if there's really a bomb,' John said.

Mary shook her head. 'You never know with these kinds of people.'

'Does he work for the church?' Sherlock asked the usher.

'No, I think he works for a charity that collects money for the church,' the usher said.

Sherlock looked at Mary. 'You're the only one he's never seen, go into the church and check whether he's there, or whether there's a camera or something like a bomb.'

'Let me bring you,' the usher said but Sherlock shook his head. 'You need to stay here so we can ask a few questions.'

Mary took her phone out of her handbag, googled Tom Walker and showed the picture to John who nodded. Then she went inside.

The church inside was even more beautiful with gigantic archways and pillars. The organ played and the people were singing a hymn. The choir were dressed in red and the clergy were dressed in white and gold, including the Dean who was leading the service. There were two large candles on either side of the altar and a large Advent Crown in front of it with the four advent candles lit. The large middle one would probably be lit at twelve, Mary suspected. The majestic looks, the sounds and the smells were truly awe inspiring.

Normally it would have been the polite way to quietly move to the back pew but that's not what Mary did. Phone in hand, she walked through the walkway between the pews, in the middle of the nave. The light of the phone illuminated her face as she honoured all the people in the pews with a long look. The looks she received back weren't exactly kind, but she didn't see Walker.

She finally went to the front pew, sat down at an empty spot and immediately turned around, looking at the people again. Her second check gave the same result; Walker wasn't attending.

He's not here, she texted to Sherlock.

Her phone bleeped with the incoming message. Camera?

The woman next to her gave her a disapproving look.

The usher had seen what Sherlock had texted. 'They're filming the service, is that what you mean?'

'Was that Walker's idea?' Sherlock asked.

The usher shrugged. 'I don't know. Shall I ask the guy to stop filming?'

'No!' Sherlock said sharply.

'Wait,' John said. 'The guy? There isn't a film crew?'

'No, just a guy with a camera and a tripod.'

John looked surprised. 'That's not very professional.'

'Is he a member of the charity?' Sherlock asked.

'I could ask.'

'Don't let the camera hear you, in fact, just get the guy over here. The camera can be alone for a bit if it's on a tripod.'

The usher went inside.

Sherlock's phone bleeped. Camera guy at the back of the church.

'What do we do? John asked. If we stop the recording, surely the bomb will go off.'

'So the answer is obvious. We don't stop it.'

The usher came back with a man in his sixties wearing black clothes. 'He's from the charity,' the usher said.

'Did Tom Walker come up with the idea?' Sherlock asked.

'Yes, it's his camera, actually,' the man said and gave him a questioning look. 'He said he had to work.' The usher smiled reassuringly.

'Did your organisation do something for Christmas?'

'Uh, yes, they were collecting money for a gift,' he slowly shook his head. 'I don't remember what gift they eventually settled on. It's usually just money for the church, you see, but this time they wanted to also give something physical. I can't quite remember what. I wasn't too involved in the whole planning of it, you see.'

Sherlock grinded his teeth as he controlled his frustration. At least they'd found the camera. They couldn't switch it off but they could move it.

He called Mary.

The church was just engaged in a moment of silent prayer when Mary's happy ringtone disturbed the peace.

'Please,' said the Dean, 'switch off your phone.' He sounded rather irritated.

Mary smiled apologetically, and then picked up her phone. 'What?!' she whispered loudly.

The Dean gestured to one of the clergy members who tapped Mary on the shoulder. 'One moment,' Mary said.

'Do you see any place where they could place a bomb?' Sherlock asked.

Mary got up, looked up and down the church and then moved to the side, so that no one would hear her whispering voice. She gestured the clergy member to follow her, which he did.

She made sure he understood her as she answered. 'As you probably know, the church is built in a cross shape, with one short end where the altar is and one long end, which is the nave where the visitors are. In the middle of the cross is the choir, who are standing on either side of the middle walkway. For maximum impact, the bomb should be placed in the middle of the cross, which is right in the middle of the choir.'

The clergy member looked at her in horror. With her free hand, she put her finger over her lips and then grabbed his sleeve.

'Listen, Sherlock,' she continued, 'there's nothing there in the middle so either he didn't get a chance to put it there or it's under the floor. I've got a clergy member here who might help us.'

She looked at him. 'Has there been any building done?'

He shook his head.

'Okay, no building, she said, it must be somewhere else.'

Sherlock looked at the usher and the cameraman. He wanted to get inside the church and now he could. The camera probably sent a signal to Walker's laptop or phone or something. He'd just have to make sure the camera didn't catch anything visual or audible that could tip Walker of his presence.

'You,' he pointed at the cameraman. 'That camera must change position. It may not see or hear anything unusual. Move the camera forward, through the church, as if it were part of the recording and place it in the middle of the choir, towards the altar.' He looked the man straight into the eyes. 'Do not let it see me or we're all dead, do you understand?'

The man nodded, his hands were trembling now.

'Mary?' Sherlock asked. 'Give me that clergy person.'

'Hello?' said a whispering male voice.

'You heard about the bomb, right? There will be a camera moving into the choir. That choir needs to make a lot of noise. When they're singing, we can evacuate the church. Speak to whoever is running the service.'

'Okay.'

Sherlock turned to the usher. 'When the choir is singing, start evacuating, last pews first.'

The usher nodded. Sherlock looked at John. 'Let's go inside.'

They followed the cameraman into the church, the Dean had just begun with his sermon, taking care to stay behind the camera. The cameraman took up the camera and tripod and slowly walked towards the front, filming the people left and right. Sherlock thought that must be a rather shaky image. After he had talked about the Christmas theme of Christ made flesh, the idea that the supernatural could be natural after all, and thereby defining itself out of existence, the Dean was now contrasting it with the Easter story of doubting Thomas, a story Sherlock thought to be idiotic at best. They followed the cameraman at a safe distance.

The Dean looked up at the cameraman and Sherlock and John, gave them a frown and continued the sermon. Sherlock saw a clergy member scribbling something on a piece of paper. The cameraman put the camera in the middle of the choir, facing the altar, just as the Dean said: 'Blessed are those who do not see and yet believe.' Sherlock looked at John and pulled a face. With that attitude no crime would ever be solved.

The clergy member went over to the Dean and gave him the piece of paper. The Dean interrupted the sermon to read it. When he finished, he looked up at Sherlock and John. Sherlock gestured him to continue. He continued the sermon but brought it to an end as quickly as possible.

'And now,' he said. 'Choir and congregation, please turn your pages to Oh come, All Ye Faithful. It's on the second last page.'

There was some mumbling, the sound of turning pages and several confused looks, because this was not what it said in the liturgy. Then, after a few awkward moments of silence, the organ played the first note and the choir started the song.

Sherlock looked at the back and saw the usher and several clergy members evacuating the last pews. His heart raced; as soon as Walker would hear anything, the whole thing would be over. He focused, now seeing every detail, every wrinkle in the people's clothing, every stain on the floor, every piece of damage to the wooden pews, every needle of the Advent Crown, every drop of wax from the candles.

He remembered the chocolates: church and bell they had found, they referred to the location, the nativity scene for the subject of the sermon, yule log and Christmas cracker for the bomb. A Christmas cracker was always pulled by two people. A clenched feeling in his chest, he opened his eyes and looked at the Advent Crown.

'A Christmas cracker is always pulled by two people,' he mumbled to John. 'They really shouldn't light that fifth candle.'

John looked and Sherlock knew that he saw the same thing that he saw. It was a giant candle, big enough to hide several pounds of C4.

Sherlock caught the Dean's eye and nodded towards the candle. He saw the man's face whiten but otherwise, the Dean stayed in his role. The choir was now also looking at him, confused looks as they saw the people leaving. The church was now half empty, people were mumbling, they didn't understand what was going on. The clergy did their best to convey a sense of urgency through their looks and gestured people to be quiet. Sherlock gestured to the choir to sing more loudly. Then he saw Miranda Shepherd. She had recognised him. Her face looked tense, she knew something bad was about to happen. Then she sang louder than everyone else, the people surrounding her doing their best to match her volume.

Mary walked up, carefully staying behind the camera, and stood next to John. Sherlock gestured for the cameraman to leave and grabbed the camera. He pointed it to the altar and slowly zoomed in. Now the altar filled the whole picture. He pointed at the clergy and gestured them to leave quietly. They looked at the Dean who nodded. They left, now it was just Sherlock, John, Mary, the Dean and the choir.

Sherlock went to the first candle he saw and blew it out, John and Mary followed his example until all candles were out. The choir got to the end of the song and looked at them.

The Dean took over. 'Now, there will be five minutes of silent prayer, please sit down,' he said, while gesturing for the choir to leave. While the choir tip toed to the exit, Sherlock's phone rang. The caller ID said Lestrade.

'And please turn off your mobile phones,' the Dean said, completely in character, 'this must be obvious by now.'

Sherlock took a picture of the fifth candle and sent it to Lestrade. Then the four of them also quietly made their way to the exit.

The square was empty and many cars had left. Two strange cars were parked on the side of the road, as far away from the church as possible. A man came towards them. He wore jeans, but Sherlock instantly recognised him as a policeman. Mary nodded and went to get their car. The Dean did the same with his.

'The bomb is in the centre candle of the Advent Crown,' Sherlock said to the policeman. The policeman took his radio and told his colleagues. He then turned to Sherlock, John and the Dean. 'You must all go.'

The organist and two sound technicians left the church and confirmed that they were the last ones to leave. Something that looked like a remotely controlled model tank went into the cathedral. Sherlock knew that it was a bomb disposal tool.

Mary and the Dean drove up to them. The Dean took the organist and the technicians and drove into the direction the policeman pointed him. John got in the car but Sherlock hesitated and looked back onto the square. Something wasn't right.

'On the ground!' he screamed. They ducked behind the car. A gunshot sounded. Then there was silence.

Sherlock looked under the car onto the square.

A figure walked to the middle. It was Walker. He was wearing a black suit.

'It's you!' he screamed at the car. 'How dare you.'

Sherlock suppressed the impulse to get up and answer, helped by the fact that John was holding him down by his sleeve.

'Any idea who I am?!' he screamed at them.

The policeman's radio cracked. 'It's defused,' said the voice.

Another gunshot. Sherlock saw that Walker was aiming in the air. Looking the other way, he saw the policemen in the two civilian cars. They were armed and already aiming at Walker.

'How dare you take away my revenge?' Walker screamed. 'After all I've done for the community. The ungrateful pigs.'

'Wasn't it his idea to play this game?' John whispered to Sherlock. Sherlock grinned.

'I am the authority here. That monster of a woman just left me as if I were nothing. She doesn't know what she's dealing with. She and her friends were just gossiping about me. They even got Vicky to doubt me. The stupid bitch said she would leave me. Well, she got what she deserved.' Walker looked at the place where he imagined Sherlock to be. 'And so will you,' he said and aimed.

Five gunshots, almost at the same time.

Sherlock didn't feel pain. He looked at John, checking, John looked fine as well.

More gunshots.

The two policemen were firing out of their windows.

He looked at Walker, he fired back, but then he fell over. Without even seeing it, Sherlock knew what had happened. Walker had been hit in the head.

The following morning, Sherlock woke up late. Golden light was shining through the window of his hotel room into his face. He listened but no sound emerged from John and Mary's room. He closed his eyes again and was back on the bridge in his mind palace. He cleared all the hills of objects and people. Now there was just grass, blown around by a cold wind. The train, the tracks and the nameless characters were still there.

He looked from the character on the bridge to the ones on the tracks, to the train, back to the bridge, eventually just the hills. The only thing he heard was the wind. Two situations, identical as far as costs and benefits were concerned, but with inverse solutions.

'Oh, Sherlock, why do you never pay attention when I talk about forensic pathology?' Molly was standing on his right side now, looking amused. 'Or if John talks about it for that matter, just a few weeks ago.'

John had appeared next to her. 'Disrupting emotional processing severely impairs decision making,' he said.

'Did you not remember what he was talking about?' she asked. 'There are people with brain injuries that somehow make them incapable of emotional processing.' She looked him in the eyes. 'They literally can't feel emotions, except for the most basic ones, while their ability to reason stays fully intact.'

'And that impairs their decision making?'

'To a disastrous extent. Those people end up needing constant care. You can give them a problem and they can weigh all pros and cons but then they're unable to decide which solution would be the correct one.'

'This is all very charming,' said Mycroft, who now stood on his left side, 'but we can weigh pros and cons and we can decide that we want more of the former and fewer of the latter. The problem is still a paradox.'

'Don't you see?' Molly asked. 'It's the emotional processing that decides whether a thing is good or bad, not the logical processing. This is the tool we use for our decisions. It's older than logic and not strictly logical in itself, therefore you cannot reason yourself out of this problem. The paradox is merely a feature of our deepest instincts about right and wrong. It's what connects us to all humans.'

'It's a tell.' John said. 'Struggling with this decision means that we actually have the capability to make it in the first place.'

Sherlock stared at the character on the bridge, then over the railing to the train. 'Imperfection is the only possibility.' He smirked. 'Tom would hate that.'

'Do you know why?' Mary asked.

'Because he needs to be perfect. For some reason, being imperfect is too painful.'

'Then what does he do?' Mary asked.

'He shuts himself down. He shies away from that pain and creates a grandiose fantasy. Therefore, paradoxically, self-criticism causes the fantasy of grandiosity.'

Sherlock gave Mycroft a look. Mycroft shook his head. 'Without self-criticism we'd be out of control completely.'

'Are you sure about that?' John asked.

'You're saying there's another way?'

'Do you understand?' Molly asked. 'He shuts down his own emotional processing and thus the most important part of being human itself. He turns himself into a monster.'

'It's not through our strengths that we connect to people.' Mrs Hudson smiled. 'Everyone suffers in some way, it's not what isolates us, it's what connects us.'

Sherlock looked at Mycroft who just gave him a confused look.

John pointed at Mycroft. 'He's not going anywhere. You won't be out of control.'

'He wants to be admired so desperately.' Mrs Hudson said. 'And what is this other than our deep desire to connect? Isn't it odd that he craves connection more than anything else, while in the process destroying the very part of himself that makes that possible?'

It was late in the afternoon when they finally reached London again. The weather had turned for the worse.

'What are you doing for Christmas anyway?' John asked when they pulled over at Sherlock's door.

'Where did you get the idea that I cared about Christmas?'

'Sherlock, you're not going to celebrate Christmas alone.'

'I'll be with Mrs Hudson, she's not going anywhere either.'

'Would you like to have dinner together?' Mary asked from the driver's seat. 'We're not doing much either.' She looked at John. 'We don't even have groceries because we were obsessing about the church.'

'I thought you'd take care of that,' John said.

Mary just shrugged. 'I was going to, but then we decided to go to the Cotswolds instead.' She smiled at Sherlock. 'Would you like to have takeaway with us?'

'But then Mrs Hudson would be alone,' John said. He looked at Sherlock, seemingly expecting something.

For a moment, Sherlock just stared; then he worked it out. 'Why don't you three come to my place and we have Chinese or something? Then we'll be with five people.'

Mary went to pick up the baby and Sherlock and John went inside. Mrs Hudson was happy to have them over, even if that meant that this year's Christmas dinner would be takeaway. She decided that with a few candles and decorations, even Chinese food could be festive enough.

John went upstairs but Sherlock lingered. 'Yesterday, I think you may have had a point.'

'I know, I had, dear.'

Sherlock looked at the stairs where John had just disappeared. 'I didn't really expect them… I mean, John and I had a bit of a fight earlier.'

She laughed. 'Oh, Sherlock, don't you remember? No one receives a coal in their stocking.'

She smiled and he smiled back, feeling slightly confused.

When he got into his apartment, John had boiled water, like he'd done so many times before. Sherlock took his violin and started tuning. He heard how John came to stand next to him and turned around.

John looked at Sherlock as if he wanted to say something. Sherlock looked at him expectantly.

John cleared his throat. 'Quite a case, wasn't it?'

'Yes, quite.' Sherlock stared out of the window. It was dark and drizzly.

'Not really how I envisioned Santa Claus as a kid.'

They both chuckled.

'John, I...' he stopped as he realised that he didn't have a clue how to end that sentence.

'Sometimes I make decisions that affect other people's lives. Sometimes it's a matter of life and death.'

John nodded quickly. 'I'm a doctor; I know like no one else that you can't save everyone and that you have to make choices sometimes.'

Sherlock looked outside. Three women in raincoats were walking briskly on the pavement, hurrying to get out of the rain.

'I just hate the fact that it's so difficult.'

Sherlock saw in the reflection that John smiled.

'Welcome to the human race.'

He suddenly felt uncomfortable. 'Right, eh, I just wanted you to know that.'

He turned around to see if there was anything he could do in the kitchen and was quite startled when he felt Johns hand slapping his shoulder.