When John tried to pick up his cup of tea, it wasn't there. It wasn't there in much the same way that a tiger having escaped from its enclosure at the zoo is not there: quietly, and without stripes. Mustering all the staunch resourcefulness of a beleaguered zoo-keeper, he went into the kitchen to prepare himself another drink.

However.

Upon noting that the kettle had been filled with slugs, John began to attribute a certain ominous quality to the hitherto unremarkable absence of his glorious brew. Nonplussed, but still yet undaunted, he filled a small saucepan directly from the tap, and set it on the stove. Then, when it had reached a rollicking boil, he deemed it ready to pour. So far, so good.

He inspected a bag: tea leaves only. Good show. Mug, bag, water. He closed his eyes, anticipating his forthcoming mug of brown joy.

Three minutes later, he carefully poured a measure of milk onto a small tiger.

"For Chrissake!" he yelled. "Sherlock!"

"Not now, John," was the infuriating reply, emanating from Sherlock's bedroom. "Busy!"

"But Sherlock! My cuppa's turned into a tiger!"

Sherlock appeared in the kitchen next to him with improbable speed. "A tiger? Not bad—I expect that might even turn the damn thing off." Then he was gone as quickly as he'd appeared.

Shortly thereafter, John's tea jiggled awkwardly back into existence, accompanied by what he could only describe as a sort of strobe-roaring effect. Not one to look a gift tiger in the mouth if he could possibly avoid it, he drank it down as quickly as he could and, by some freak of chance, didn't burn his tongue.

"Two to the power of one hundred thousand to one against and falling," announced Sherlock, with relief that was plain to hear.

Meanwhile, the flat had inexplicably started to tidy itself up. John peeked into the kettle and found that the slugs had disappeared.

"Two to the power of seventy five thousand to one against and falling."

John's moustache dropped off his face and morphed into a Chihuahua puppy.

"Did I ever tell you, John—two to the power of fifty thousand to one against and falling—how much I missed you when I was away? Do you... could you really... forgive me the hurt I've caused you?"

John made a face but, feeling uncharacteristically voluble, he replied in kind. "I wanted you not to be dead, you know. You were the best man I've ever known, so yes... hang on... I don't know what you're doing, Sherlock, but it's turning me into puppy dogs. Stop it."

"Three to one against and falling," Sherlock called. "Two to one against and falling. Probability factor one to one, and normality."

John felt as though he'd just come ashore after a long stint on a ship, and still had wobbly legs.

"What the hell was all that?" he demanded. "You... you cock!"

Sherlock staggered out of his bedroom with John's original cup of tea—though the mug had acquired some suspiciously tigerish stripes—and collapsed into an armchair.

"That'll teach me to invent a machine without an off-switch. An infinite improbability drive, John. Runs on a set of logic processors immersed in a Brownian motion generator—the cup of tea you so kindly lent me—and it should have run down when it reached thermal equilibrium with the environment, only against all odds, it didn't. That was very clever of you to think of turning your tea into a tiger; I realised that if I nudged the device to match the effect with the generator, it would cut itself off. There was a bit of an unexpected feedback loop, but all's well that ends well, right?"