Joan took a step towards her.

Sherlock cried out, "Watson no! She's dangerous-"

Joan thought of Mishka being twice prevented from hugging her - once by a beer bottle clashing into a cafe window, once by a grandfather clock splintering after a two storey drop - and she realised what Sherlock had done.

Nevertheless, she moved towards Mishka.

"Sherlock, I think you wanted this." Joan reached out and ripped off one of Mishka's necklaces. She stepped back quickly as the cops closed in, and held it up: a simple chain, on the end of which was a white plastic key. An unnatural looking key in a sickly white colour. A printed key.

She gave it to Gregson, who bagged it. Then she turned for another look at Mishka.

"That's not my girlfriend!" said Brad.

Mishka, who had been standing very still between two cops, gave Brad a scornful glance. She lifted a hand to her mouth, and pulled out two cheek pads. Then she tugged at the heavy back bangs hanging in her eyes. The wig came away in her hand, as did the large glasses.

"How about now?" suggested Sherlock. "Try picturing the look with a lot of bronzer and a gold wig."

A woman older than Mishka, with fine high cheekbones and an elfin black crop, stood proudly looking at Joan, and past her, at Sherlock. The geek clothes and jewellery hung on her like the props they were, and Joan saw the poise they had hidden.

Irene spoke. "Hello, Sherlock." Her voice was low and calm, with the merest trace of a European accent.

Sherlock looked at her with no expression, then spoke to Gregson. "I suggest you question this woman regarding the theft of Mr Fargo's prototype. Also, when she is in custody, please bear in mind this is a woman who can print keys."

"And if it doesn't stick?" asked Gregson. "Something tells me Ms Adler has an alibi. Her past record shows a lot of arrests and almost no convictions."

"I paid my dues to society, officer, "said Irene. "But if you wish to accuse me of some new crime, based on my possession of a decorative key, then please, be quick. I have a flight to catch."

"If you can't keep her on charges of industrial espionage," said Sherlock, "then perhaps you can charge her with breaking into my house? I can prove she was there."

He shone the black light device at Irene, and her face and hands lit up in an eerie violet colour.

Joan gasped. This woman, in the house - their home! In Sherlock's bedroom - in her bedroom?

"I like to check up on you from time to time," Irene said to Sherlock. "See what kind of company you're keeping." She turned to Joan. "I'd heard that he paid you...like the others...But you send such marvellous emails to each other. I knew you were something...different, and I confess I am only a little disappointed." She smirked, taking in Joan's bare face, cosy clothes and big boots.

For a woman dressed as a nerd, Irene gave off an incredible air of physical superiority, as if she wore a beautiful gown which only the privileged could see.

Joan said, "I don't exist to please or disappoint you." She paused. "Or anyone."

"Let's move this along," said Gregson. "Mr Fargo, if you can also accompany us to the precinct..."

"I trust you can handle it from here," Sherlock said to Gregson, who gave an upwards nod.

Sherlock glanced at Fargo and Brad, who seemed shocked. Brad was staring wide eyed at Irene.

Sherlock looked at her too, and his face was quite still.

Then he gestured towards the stairs. "Watson."

She nodded, and they made for the street.

xxxx

"How did you know she would steal the hub?" Joan asked. They were on the street, in gritty air, walking back to the brownstone. Joan had still not been able to say the name, Irene, out loud to him. She honestly did not know how he would react.

Sherlock was walking hunched, hands in pockets. "I didn't." He stole a glance at Joan. "If I'd realised sooner, I would have prevented it. But I wasted a lot of time because of the letter."

He frowned, scuffled his feet. "When I first got it I thought she meant you. That she was trying to...get to..you."

Joan thought of the letter. 'I'm in town to get hold of this hot new thing...' In spite of herself she almost laughed. "I suppose that's some sort of compliment."

"I thought she would break in to the house, maybe bug the place to try and find out our relationship. Evidently her earlier research about why you were living with me had left her confused. I never realised she had hacked your email."

"I had trouble for a few days even before I met Mishka," Joan recalled.

"I set up the marker primarily so that I would know if she had been in the house." Sherlock grimaced. "Which she has, incidentally. And quite extensively. That's why I had to have the place cleaned after I tested the perfume on you. Even though the second batch contained a different marker, I didn't want any confusion with your traces in the house."

Joan digested this. They walked a few yards in silence, then she said, "Does it strike you as creepy and chauvinistic to mark the women in your life so that you can tell exactly where they've been?"

Sherlock watched the pavement. "Not in these circumstances, no."

"Right." Joan folded her arms. She stopped square in front of him. "What about giving someone the common courtesy of letting them know a stranger has been in their home? What - where? In the den? The bathroom? In... my room?"

Sherlock looked all around and then met her gaze. "Everywhere. She was all over the house."

"Oh!"

Joan whirled round and stomped off.

Sherlock caught up with her.

She walked, face set, not looking at him. He had not shared any of this with her, including the danger she might have been in. He had been cold...

She thought of the night he had held her, in his bed, without a word. Silent in case that woman was listening.

"Watson. The cleaners will be back later. I've already organized a hotel for us," he waved his phone at her, "and, and," peering at her, "and she knows nothing more about you now than she did three weeks ago. This -" he flicked his fingers between himself and her -"this, is unknowable to someone like that. Incomprehensible. She simply does not have the capacity."

Joan narrowed her eyes.

She carried on walking, and after a moment, so did he.

xxxx

Late evening. Joan had given her notebook to Sherlock with instructions to "Make it work properly with nobody snooping in my personal stuff. Including you." She had spent the rest of the day alone, ignoring Sherlock's updates on progress with the Fargo case and the state of the brownstone.

Now they were standing in the thick-carpeted corridor of the hotel, outside the rooms Sherlock had reserved for them.

"Watson, you know I don't do romance, involvement, drama."

"I'm perfectly aware of this."

"I don't believe in love."

"I know. It's a chemical reaction manufactured in the brain to engender genetically useful procreation. I know." She had had this conversation with him a dozen times in her head. Now, here, there was no need to spell it out. There never had been.

Sherlock grimaced, reached warily for her shoulder.

"But I'm not incapable of forming attachments, Joan. I do become attached." He was gazing at her with that peculiar intensity which defined him: both knowing and unworldly at once.

"I know what we have," Joan told him. "Whatever it is. I'm fine with it. But I won't be experimented on, and I will not be kept in the dark when either of us could be in danger.

She felt compelled to add, "I'm not proud of the way I've been acting lately. For a moment I thought my life would be better if I behaved a little more...carelessly. As if I didn't believe in love either."

"You're not a careless person," he said.

She shook her head.

"She was nothing like you,' he said. He held her shoulders, leaned in and kissed her gently, looking into her eyes.

Technique, Joan thought. Sherlock knows that this is how men make it up to women. It's just technique. And how could anybody know the difference?

But there was something in his face as he leaned back to see her reaction, something troubled. Was it fear?

She was more disturbed by the idea of his attachment to her, than she could process just then.

Joan kissed his jawline, then slipped away to her room alone.

Attachment would have to wait.

The End