Someone is pranking the 12th Precinct and Beckett is on the case.

Sleep-deprived, bleary-eyed, and late for work, Kate Beckett stumbled as the heel of her shoe caught on the gap as she exited the elevator. Castle wasn't with her-he was due back later today from a writing tour. If he had been, he would have turned to her with that twinkle in his eye and said, "Mind the gap," imitating the classic announcement from the London Underground.

Now that they they'd been together for a while, Beckett found she didn't sleep well when Castle was away. A disturbing thought in some ways-what did it say about her independence?-and one that she would never admit. At least, not yet. Pushing that thought aside, she mustered as much dignity as she could and strode to her desk, wincing slightly. The new shoes had been a mistake; they were already pinching her feet. She should have broken them in on the weekend.

Sitting down at her desk with a sigh of relief, Beckett closed her eyes, anticipating the sheer pleasure of taking the weight off her feet.

The long, loud sound of a fart made her relief short-lived. As her eyes popped wide open in shock, the precinct became dead quiet. For a moment you could have heard a pin drop. All eyes were fixed in her direction.

Beckett, her face red with a mixture of embarrassment and anger, stood, picked up the whoopee cushion and brandished it. The staff burst into riotous laughter. Some were doubled over, holding their bellies. Others turned away to disguise their reaction, but the hands over their mouths and shaking shoulders gave them away.

"Alright," Beckett yelled over the din, "whose idea was this?"

The laughter slowly faded, but no one stepped up to claim responsibility. Beckett strode over to Ryan and Esposito.

"It was one of you two, wasn't it?" she said. "Admit it."

Ryan, dabbing tears from his eyes, said, "Us? Do you think we'd dare? That we'd be so foolhardy?"

Esposito nodded in agreement. "Sorry, Detective, not us. You have to admit, though, it was pretty funny. Someone clearly remembered that it's April Fools."

"Funny," she repeated as she headed back to her desk. "We'll see if whoever did this thinks its funny when I get my hands on them."

Ryan and Esposito shared a look. "Someone's in for a world of hurt," Esposito said. Ryan exhaled and nodded in agreement.

Just then, the bulb over Esposito's chair when out. He and Ryan looked up at it. "Maybe it just needs tightening," Ryan suggested.

"Maybe," agreed Esposito. He pulled his chair over and stood on it. But as he reached for the light fixture, the chair collapsed under him and Esposito fell to the floor, his legs sliding out in front of him, leaving him sitting in shock with the remains of his ruined chair scattered about him.

Ryan scooted over and helped him up. "You OK, bro?"

"Yeah," said Esposito. "Took me by surprise is all."

Ryan knelt down. "Look at this. These bolts have been partly unscrewed. Someone sabotaged your chair."

Beckett had come over and was kneeling beside Ryan. "Probably the same someone who put that… thing on my chair."

Esposito and Beckett turned to Ryan.

"What?" Ryan asked.

"Admit it, Bro. It was your idea to tighten the bulb. You wanted me to stand on that chair."

"Come on, Jav, it wasn't me. When was the last time I pulled a prank?"

Esposito regarded him steadily. "He has a point," he said finally. "I think he's telling the truth."

"Maybe," said Beckett. "But I'd keep an eye on him just the same."

Ryan sat down at his desk in relief and took a drink of his coffee. Then, shaking his head with disgust, he put the cup down and stood again. "Ugh. What on earth was that?"

"Wait a minute," Esposito said. "Open your mouth again."

Esposito and Beckett looked at him, then at each other, and then burst out laughing.

"What?" Ryan said.

"Bro, you feeling blue today?" Esposito asked between laughs.

Beckett covered her mouth until she regained her composure. "Your tongue," she said. "It's blue."

Ryan dashed to the men's room. He returned a couple of minutes later, disgust written on his face. "It won't come out," he said.

"I guess it wasn't him after all," Esposito said.

"Yeah, but somebody did this," said Beckett. "Someone with a pretty juvenile sense of humour."

"Hi guys," said Castle as he got off the elevator. "Got back early and thought I'd see if I…" he saw the looks on their faces and stopped. "... missed anything."

Beckett, Ryan and Esposito approached Castle with slow, menacing steps.

"Um, guys?" said Castle.

With the three of them standing side-by-side, inches from Castle, Esposito asked, "We going to do this?"

"Hell yes," Ryan answered.

"Cuff him," ordered Beckett, her face expressionless. "Take him to interrogation room one."

"Wait, what?" Castle said as Esposito pulled Castle's arms behind his back. "Really?"

"Richard Castle," said Esposito as he slipped on the handcuffs, "you have the right to remain silent, but you may have the crap beaten out of you. Anything you say will be used against you. You do not have the right to an attorney. Let's go."

"But… what did I do? I didn't do anything! Beckett? Beckett, come on. Ryan? What happened to your tongue? Ow! Not so hard."

Beckett maintained stony silence as Esposito escorted Castle to the interrogation room.

Fifteen minutes later, the three of them regarded Castle through the one-way glass. He was still twitching about, pulling on his cuffs, calling for Beckett to see reason.

"Think he's stewed long enough?" Ryan asked.

Beckett nodded. "Let's go."

The three of them entered the room and sat opposite Castle. No one said anything.

"Is anyone going to tell me what this is about?" Castle asked.

"Mr. Castle, where were you earlier this morning?" Beckett asked.

"Mr. Castle? Really?" Castle said.

"Just answer the question," said Ryan.

Castle swallowed. "The plane landed at 5. I took a red-eye. I went home, showered and changed, checked my mail, then came here."

"Can anyone corroborate your story?" Beckett asked.

"My story?" said Castle. "No. Alexis is at college and Mom is out of town. You know that."

"So you have no alibi," Esposito said.

"Alibi for what?" Castle asked.

"Interfering with police business is a serious crime. Did you know that?" Beckett said.

"Look, just what is it you think I've done?"

"You could be looking at jail time," continued Beckett.

Castle was quiet a moment. "I'm guessing from the colour of Ryan's tongue that someone's been playing pranks. Is that what this is about? You think I did it?"

"You had the means and opportunity," said Ryan. "And as for motive, well, we know all about your twisted sense of humour."

Before Castle could reply, Captain Gates poked her head in the room. "Do you have nothing better to do than to interfere with the rights of New York City citizens?" she asked.

Beckett hesitated, then said, "Sir, Mr. Castle's pranks may constitute interfering with police business."

"And do you think that Mr. Castle is the only one with a sense of humour around here?"

Beckett, Ryan and Esposito gaped.

"Sir," said Beckett when she recovered, "you don't mean that you…"

"What I mean, Detective, is that the only ones interfering with police business are you three, for not doing your jobs. It's noon. Now get to work."

"Yes, sir," Beckett mumbled, her face slightly flushed. "Uncuff him," she said.

"Sorry, bro," Esposito said as he released Castle. "You know how it is."

"What did she mean by, 'It's noon'?" Ryan asked.

Castle, rubbing his wrists said. "It's the old English rhyme. At noon you say, April Fools is past and gone. You're the fool and I am none."

Esposito and Ryan left, leaving Castle, his arms folded, regarding Beckett, whose eyes were downcast.

"There's going to be payback, isn't there?" she said.

"Hell yes," said Castle.