He was staring at the patchwork of pictures and notes he'd pinned to the tapestry, trying to find a pattern that might help him solve the case. Well, two separate cases, actually.
"Have you ever seen the Queen?" Jack asked from the other end of the room.
"Nope," he replied absently, his mind busy following three separate trains of thoughts.
"Uncle John says you've been to Buckingham Palace. And you stole an ashtray too."
"The Queen has plenty of them, she wouldn't even notice that one was missing."
"But what if she finds out? Would she lock you up in the Tower?"
He frowned, removed a picture, then pinned it in a different position. "I doubt it. It's been years ago anyway."
"Do you still have it?"
"Have – what?"
"The ashtray."
"Of course. It's – somewhere," he said vaguely, gesturing to the flat at large. "You can keep it if you're able to find it."
"Cool," the little boy exclaimed in delight, before rushing out of the room.
Speaking of ashtrays, he could kill for a cigarette now. If only he could find his stash and sneak downstairs before Jack was back – well, that would be truly marvellous.
"It's no use looking for your cigarettes," the boy warned him from the next room, and he paused – a half-annoyed, half-amused smirk spreading on his face.
"Who says I was?" he called in defiance, but he could almost picture the kid rolling his eyes at the dullness of the question.
"You've been working on the same case for over a week, and I've just mentioned ashtrays. What would you deduce, Dad?"
"All right, you win. But why did you say it's no use?"
"Mom says you shouldn't smoke, so I used them for an experiment of mine."
"Oh, did you really?" he all but chuckled. This whole situation reminded him of a particularly nasty trick he'd played on his brother when they were still in their teens; that had probably been the first and last time he'd seen Mycroft lose his cool, something that was an achievement in itself.
"Here it is," the boy announced merrily, banging into the room with his new trophy.
For a moment there he was sorely tempted to tell the boy that he'd actually had the nerve to show up in Buckingham Palace wearing nothing but a sheet, but he suspected that was something neither John nor Molly would approve.
Then Jack jumped onto the sofa, took a good look at his notes and swapped two of the pictures.
"I think it works better this way," the boy said cheerfully, and the pattern he'd been chasing for days was suddenly clear before his eyes.
"There aren't two cases, it's just one," he claimed triumphantly, wondering how he hadn't been able to see it before.
"I knew you would work that out eventually," Jack nodded, as if he was talking to a child. "May I have some chocolate now?"