This story arose from a discussion with Bahamut Slayer. All complaints should be directed to them.

Chapter 1

"What have the twins done now?" Beckett wailed, after their terrorist twosome were safely in bed, having exhausted themselves in creating terror, horror, and havoc. Or alternatively, by having a normal day for the Castle clan.

"I don't know. They've only been in daycare two months."

"Surely they didn't change."

"No," Castle said very reassuringly, and hugged her. "We'd have known about that straight away. Along with every news service in the world."

"That wasn't as reassuring as it could have been," Beckett grumbled.

"It's probably something like hitting or biting. Normal things for nearly-three year olds."

"Not if it's with claws."

"Don't be silly. No changes, remember?"

"I wouldn't put it past them to work out a half-change." They had surely worked out every other method of causing trouble. Why would they ignore that possibility?

"If we haven't, they won't. Let's just give thanks that they're behaving."

"In that way. Not any other." They never behaved. She'd thought the twos were supposed to be terrible. The threes were looking like being worse.

He smiled at her, which improved her mood. The only thing that improved her mood faster than Castle's open, happy smile was seeing the twins fall asleep. "Now, how about some misbehaving?"

She kissed him hard. "Sounds like fun," she enticed. "Who shall we be?"

Castle's huge panther appeared. Beckett played with his ears for a few moments, and then became her own sleek lethality and strutted to the bedroom. By the time Castle got there, seconds later, she was her human self again, lithe, beautiful – and naked.

After that, they didn't worry about the parent-daycare interview until they woke.

"Why does Miss Carter want to talk to us?" Beckett asked the twins.

"Don't know."

Beckett knew this to be a lie. Petra's conscious look and sudden concentration on her breakfast – as a child, which was the product of months of reinforcement and food withdrawal until she was human – was a dead giveaway.

"Did you hurt anyone?" Castle asked.

"NO! Hitting naughty." That never stopped Petra trying: all that she worried about was not being caught.

"Did you, Davy-boy?"

"No."

The adults got no further in finding out the problem before it was time to depart for the meeting. Both of them were nervous, which was quite ridiculous given that they were respectable, mature, professional people. In Castle's case, that description should have been prefixed with the word now. And possibly usually. Or sometimes.

"I used to feel like this with Alexis. As if it had been me who'd done something wrong."

"I thought Alexis never did anything wrong?"

"She didn't. But" –

"But you did."

"Daddy naughty?" Petra asked hopefully. Beckett was sure this was to divert blame from whatever she or David – though David was a far less likely option for thinking up dreadful deeds, while being a very likely candidate for being caught – had done.

"No, Daddy has not been naughty," she said firmly.

"Since last night," Castle whispered in her ear. "And you were pretty naughty too." Beckett elbowed him in the midriff. He oofed.

"What happen?"

"Nothing."

"Daddy hurt?"

"Nope. Daddy's fine." But he won't be if he carries on like that, Beckett thought. The subway was not the place for salacious suggestions. She glared at him. Castle smiled sweetly with a distinct edge of you know you like it. Petra – it was always Petra – looked at her parents.

"Daddy kiss Mommy now."

"What?" her parents squeaked.

"Daddy always kiss Mommy when she cross. Make 'noyy better."

"Noyy?"

"Cross."

"Annoyance," Castle guessed.

"Yes. 'Noyy."

"Say "an-noy-ance."

"An... noyy...a. Noyya!" she said triumphantly. Castle sagged. Trying to teach the twins proper pronunciation always failed. Beckett was sure it was deliberate on their part, to be annoying, but Castle's distress at their failure was quite amusing.

"Annoy-se!" David tried.

Petra glared at him. "Annoyas!" she attempted. David smirked, and as ever, Petra reacted. "Nasty!" she screeched.

"Shush!" Beckett said. "No shouting on the subway. Inside voice."

Petra subsided. When Beckett used that tone, it meant trouble. That did not mean that Petra always complied, but fortunately today she did. Threatening one's infant in public tended to result in unfortunate consequences, quite frequently for the public.

The daycare centre was reached with only a modicum of fuss and the usual ten million repetitions of hold my hand, don't run off, and the like. Petra and David were divested of their coats and hats, and sent off to play. Shortly, the sounds of Petra organising the others were heard. Her parents ignored it. They had decided on daycare so that Petra couldn't exercise her not-at-all latent dictatorial tendencies solely on David. All that had happened was that she was developing a talent for directing small armies, including all the other small – and not so small - children. It appeared that a larger stage had merely provided her with more opportunity to – er – manage. That had not been the plan. The plan had been that others would try to organise Petra. It wasn't working. Petra's personality easily overpowered all known groups of children.

"Mr and Mrs Castle," the keyworker said. "I'm Jada Carter." They knew that. Of course they knew who the twins' keyworker was. "I'm so glad you could come in."

Beckett didn't appreciate being called Mrs Castle by anyone, except Castle himself, at any time. She was Detective Beckett. She considered saying so, and decided that this discussion was going to be bad enough without adding unnecessary difficulties. Jada caught her expression, and moved very swiftly on.

"We're having some concerns about Petra," she said. Petra's long-suffering parents exchanged oh-shit-what-now glances. "It's very normal for small children to indulge in imaginative play, but Petra seems to be unable to make any distinction between her imagined scenarios and reality."

"In what way?"

"She insists that she's a cat. A black cat. And that both of you are also cats, and David. She is also convinced that all four of you are panthers."

"Oh."

Oh shit oh shit oh shit.

"David isn't nearly as insistent, but he seems to have been caught up in his sister's game, and can be almost as...um... imaginative. Petra is very" – she clearly searched for a less offensive word than tyrannical – "persuasive."

"But you said imaginative play was normal?" Beckett said very neutrally.

"Well, yes, but" –

"And of course I am a fiction writer, and Petra and David hear a lot of stories."

"Well, yes, but" –

"Isn't this just another small-child game?"

"Mr and Mrs Castle," Jada said, as if they were themselves small children. "Petra and David are not able to make the usual distinctions between them being children and them being cats. I am a childcare professional" – there was a very strong implication of and you are not: you are merely parents and therefore know nothing – "and this is very worrying even at this stage."

You don't have a clue how worrying, they thought together.

"I believe that both children, but especially Petra, should be assessed by a psychiatrist."

"A shrink?" Castle squawked.

"A psychiatrist. Yes. With proper assessment now, this won't become a problem later. We'll do all we can to support you. Let me know what you decide."

Probably as a result of Beckett's visibly rising fury, Jada pushed them out of the daycare centre as quickly as possible, to leave them standing on the sidewalk.

"I think I need coffee," Castle said.

"I think I need whisky," Beckett replied.

"At least they haven't actually changed."

"I wouldn't put that past Petra, just so she could prove the point."

"Oh God."

"Yep."

"Let's go home."

Back in the loft, they stared gloomily at each other. "Now what?"

"Apart from whisky?"

"Yeah."

"Guess we'd better start looking up a shrink."

"Back to medical confidentiality."

"Yeah. Great."

"Dr Maine was just fine," Castle said rather absently. "Um..." Beckett had a feeling of sudden dread at his dreamy expression. "Now the twins are older...um..."

"Absolutely not. No more. None."

"Oh." He tried to look adorable.

"We've just got some sort of normality and sleep back, and you want to ensure we never sleep again? Or get to do anything else?"

"But..."

"And what if it were twins again? Or triplets? Or freaking quads? You know it could be a litter!" Beckett's voice was rising rapidly. "And I hated being pregnant and morning sickness and you'd have to deal with it all over again" –

Castle paled at the memory. "No. It's not a good idea. No. I should never have thought of it. I won't mention it again. Never ever. Never." He extracted his feet from his mouth and turned into his cat, to butt adorably at Beckett and possibly be petted. She glared at him.

"Turning into a cat isn't going to help you here," she growled. He changed back. "We need to find a shrink."

Some focused research later, they had a list of top-quality psychiatrists who would treat children: at least until they had become acquainted with the terrorist twins.

"Okay," Castle sighed. "This guy seems like the best. He's older, so he'll have seen it all. He's got qualifications coming out of his ears, so he'll respect confidentiality."

"I'll get Gates to give me a day off as soon as we've got an appointment. She'll understand if it's about the twins."

"She won't want to visit, will she?"

"Probably."

Castle mumped. Gates's visits were invariably disconcertingly disapproving, though the twins loved her and she, astonishingly, loved the twins. Sadly, her view of Castle was as acerbically dyspeptic as on the day they had met, which never failed to rile Beckett. Castle and Beckett's wine consumption after her visits, which were uncomfortably frequent, reached levels best described as unhealthy.

"I'll explain to her. You call this Dr Burke and set something up. Better make it for two to three hours. Call me when you're done and I'll see Gates. Ugh."

"Better ensure we've got strong liquor."

"For us or him?"

"Both."

Beckett whisked off to get to work before the day was entirely wasted. Castle ambled in the direction of his study and the phone, and contemplated his laptop and Dr Burke's number with extreme dislike. Despite the relative success of telling their close family and friends some months ago, since when not a single word had leaked of their – er – additional genetics; he felt very strongly that the whole house of cards could come tumbling down at any moment.

He dialled.

"Dr Burke's practice," said a very refined voice.

"Hey. This is Richard Castle. I'd like to make an appointment with Dr Burke to see our two children. The daycare centre has expressed some concerns..."

"Certainly." The receptionist took some pertinent details. "Dr Burke normally expects a first appointment with children to take half a day." There was some clicking. "He could see you all next Monday morning." It was Thursday. "Most fortunately, there was a cancellation. Dr Burke is very busy. Could I have your name again?"

"Castle."

"Ah yes – Richard Castle? The writer? Is your wife attending as well? I'd love to meet the inspiration for Nikki Heat. And you, of course," she added.

"Yes, she will," Castle said, rather deflated by the receptionist's clear preference for Beckett.

"Wonderful! We'll see you at 8.30 on Monday morning. Thank you."

"Thanks. Bye."

He rapidly texted Beckett, and received a quick smiling emoji in return.

"Sir? Do you have a moment?"

Gates regarded Beckett very sceptically. "Is this personal or professional, Detective?"

"Personal, sir. It's the twins."

Gates's expression softened. "Shut the door."

"Thank you, sir."

"What's the issue?"

"The daycare centre have recommended that the twins see a shrink," Beckett said baldly, "because they keep insisting that they're cats."

Gates's stern face cracked slightly. "I see. You can hardly explain that they actually are cats, of course."

"No."

"Mm. And why is this relevant now?"

"We've managed to get an appointment for Monday, and I wanted to request leave for that day."

"Mm. That is remarkably quick. Are you sure you are seeing a reputable person?"

Beckett bridled. "Dr Carter Burke."

Gates choked on the mouthful of coffee she'd just taken. "Carter Burke? Good Lord. How did you manage that?"

"Huh?"

"You may not be aware that my husband is a psychologist. Dr Burke is a very well regarded psychiatrist indeed. You will be in safe hands." Gates's iron control cracked. "But I would give a great deal to see his face on being presented with your...issues." She calmed herself. "You may have leave on Monday. I should like to see the twins on Thursday, with my husband. Dismissed."

Beckett's feet took her out of Gates's office before her brain caught up. This was, regrettably, common. Gates's demeanour regularly reduced everyone to terrified horror, and even Beckett was not immune. She normally caught up with the sting in the tail of the discussion some moments after she had returned to her desk, and today was no exception. Gates and Mr Gates? Or should that be Captain and Dr Gates? Both of them? Oh God. Oh God. And Mr Gates was a psychologist? And they were visiting? Oh God.

"Oh God," Castle said pathetically when he heard. "Another shrink?"

Beckett snuggled in, while the twins created havoc all around them. "He'll have a field day," she said, as Petra changed to panther and swiped at David, who promptly tried to pull her tail. There were twin shrieks of rage, and playing turned into a full-on fight. Despite a strong desire to leave them to kill each other, possibly not metaphorically, their parents waded in to pull the troublesome twosome apart and administer separate justice and time out.

After Petra had destroyed the playpens – and learned how to open doors – time outs were now dealt with by putting one twin in the spare room and one in the twins' bedroom. To avoid any unnecessary howling, the rooms were alternated. To avoid escape, the parents supervised the closed doors. On particularly bad days, their only adult time, until much later on, when they were generally too tired to take advantage of it, was as they sat together on the stairs. Children, Beckett had frequently thought, were an extremely effective contraceptive. Now there was a thought. Now that the nights were darker, it was time for O'Leary to babysit so that she and Castle could go and prowl through Central Park for an evening: murdering (but not eating) the squirrels, and terrorising any lowlifes. Such gentle amusements invariably reduced their stress levels, and the occasional articles in the press suggesting panthers in NYC were a small price to pay.

Petra was deposited in the twins' room, David in the spare room. Howls of misery rent the air. The twins fought almost non-stop when together, but bawled absolutely non-stop when separated, which was why they were now sharing a queen-size bed. The cot had become far too small, but the twins wouldn't be parted, and it wasn't a fight their parents were prepared to have. Now that they were almost three, they could sleep in a proper bed. Frequently, a late-night check disclosed two little black kittens, or cubs, rather than two little humans: though whatever the form, they were snuggled together in an adorable (when asleep) heap. Equally frequently, there was a late night miaowing at the (now double-height, chicken-wire reinforced and inward sloping) stairgate. Castle and Beckett had learned to ignore that, though it did tend to ruin any mood which they might have been attempting to enjoy.

"Shush!" Beckett said to Petra. "You were fighting, so you get time out."

"David fighting. Not me."

"Yes, you were. Both of you were fighting. Both of you get time out."

"Wasn't me. Not fair."

Petra turned her back on her mother and sulked. That was just fine. When she was sulking she wasn't arguing, screeching or destroying things. Beckett slipped out, breathed out, and sat down on the stairs next to Castle.

"Tell me again why we don't just call in the UN Peacekeepers?"

"Because they'd run screaming."

"We could hire them out as the UN Peacekeepers."

"Nice thought, but someone would call Child Services."

"Oh. Just for a day?" she said hopefully.

"Don't think so."

Beckett leant her head on Castle's shoulder, and they waited for time to be up, passing such time by indulging in a rather lengthy kiss and tucking together.

"Where we going?"

"We're going to meet a new friend."

Petra regarded her parents suspiciously. David bounced. "New f'iend?" he chirped. "Boy?"

"Yes."

"Want a girl!" Petra wailed, scenting unfairness, which she could detect (whether real or not) at approximately one mile's distance.

"This new friend is a boy."

"Don't want a boy. Boys nasty."

David lunged for her. Castle caught him and swung him up to his shoulder. "No fighting."

They drove to Dr Burke's Midtown practice. It seemed easier than stopping a free fight in a crowded subway train.

"Okay, we're here. Behave nicely, please."

"Yes, Mommy."

Beckett didn't believe that for a second. She took Petra's hand, Castle took David's, and they progressed to the correct floor.

The practice reception contained an austere, but expensive, receptionist's desk, occupied by an austere but undoubtedly expensively put together receptionist. There were a comfortable couch and some armchairs, which the twins were eyeing up for their potential to be used as a climbing frame. The receptionist emitted a cooing noise, which would undoubtedly be replaced by horrified tutting on longer – that was to say, more than ninety seconds – acquaintance.

Petra decided to be cute. No doubt she wanted something. Her parents wanted whiskey, but at eight-twenty a.m. that was inappropriate.

"H'lo," she cheeped. "I Petra. This Mommy and Daddy."

"Who's that?" asked the receptionist, as David ambled up.

"Boy. Not like boys."

"I David." David batted his eyelashes and looked cute.

"Well, aren't you both just adorable."

"Hey, we're the Castles. We have an eight-thirty appointment with Dr Burke?"

"Of course." The receptionist looked at them. "You're Nikki Heat!"

"No!" said Petra. "That Mommy. Not Sticky Eat."

Beckett womanfully controlled her face at Castle's expression. It was exceedingly difficult.

"Mommy a p'lice 'tec-ive."

"Yes," said the receptionist, who was also trying not to laugh and not entirely succeeding. "Your mommy and daddy are famous."

"Not famous. Mommy an' Daddy. Mine."

"Mine too," complained David.

"Mine first."

This was technically true, since Petra had arrived before David. However, it wasn't allowable.

"You share us." Petra glared. "No glaring."

Before the twins could develop their argument further, which would include fighting, a tall, dark-skinned man of at least sixty appeared from a door.

"The Castle family?" he enquired. "Please come in."

The twins regarded this interesting new person with dual piercing glares, and wandered up, followed by their parents. The door to the consulting room shut behind the four of them, which meant that the receptionist could release her laughter in solitude.

"New friend!" David chirped happily, bouncing up to the man. Petra regarded him with a suspicious glare last seen being used by her mother in Interrogation One.

"I am Dr Burke," he said.

Petra glared harder. "Doc'or? I not sick. No doc'or. Doc'or nasty."

"Doctor," Castle corrected, ignoring the main point. Dr Burke raised an eyebrow. Petra didn't diminish her glare one iota.

"Shall I take a history, and then we may begin?" Dr Burke said smoothly. David wandered up to his desk and tugged hopefully at Dr Burke's leg. Dr Burke suavely turned him around. "Please go to your father." Astonishingly, David did exactly what he was told. Petra, by contrast, sat down by the side of his desk with her small legs crossed in best daycare style, and stared coldly at him. It was really quite disconcerting.

"Mr Castle and Detective Beckett, and your two children – fraternal twins – Petra and David."

"That's right."

Dr Burke took a brief history. He was somewhat intrigued as to why the Castle family had approached him with such unwonted urgency. Their twins were not presenting with any immediately evident behaviours, nor were their parents describing anything untoward as yet.

"Why have you requested this appointment?"

"The twins' daycare centre staff are concerned that they are unable to distinguish reality from their imaginative play," Mr Castle said.

How odd. Detective Beckett had clearly stopped herself adding to that comment.

"Mm," Dr Burke said, steepling his fingers. "May I talk with your twins to see how they play?"

"Sure."

Dr Burke was quite convinced that a relevant matter was being concealed from him. However, he was not concerned. That was perfectly usual, and would be remedied during the session.

"Perhaps you would appreciate some coffee while I become acquainted with your children?"

"That would be great, thanks."

Detective Beckett perused the room. "Is there anywhere we can put the mugs out of the way? Once they start to play things can get a bit lively."

Dr Burke noted that. Lively was all too frequently a synonym for destructive. Still, he had seen that particular presentation many times, and could provide strategies to mitigate the issues. In the worst cases, medication might be required. That, too, he could provide.

"To your right is a high shelf, for that purpose."

"Thanks."

Dr Burke left to instruct the receptionist to bring coffee for the two adults, and shortly returned.

Thank you to all readers and reviewers.

On this day, September 11th 17 years ago, an atrocity occurred. #NeverForget.