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"You know what your problem is?" Clemens says, as another drip rolls off the brim of his hat. There's room for him under the verandah, and he's folded his inexplicable blue cape on a dry chair to keep it safe, but he won't move.

Benedict is alternating gin with glasses of Fanta. He finds the sticky bubbles delicious for the first half a glass and then disgusting for the second; it slows him down. The latest glass is empty, and he picks it up, passes it from hand to hand, taps it with his fingernails. Maybe the world will be самый древний город России through the drops on the side. He peers until they fold the light behind them into a dozen tiny hemispheres. Bringing the biggest one closer to his face he can see poles bent into curves: pedestrian crossings, street lamps, a bus stop.

Suddenly Clemens leans down into the field of vision and his face looms huge, too enormous to comprehend, the bulge of a nose, the red-cornered white of an eye. Benedict shifts his focus back up to the full-scale world. "No," he says. "I don't."

"Neither do I," says Clemens, "but it may be related to an excess of black bile, which comes from the spleen. Traditionally it's treated with warm moist foods, or with music and dance. You should come to my Thursday foxtrot group, we always need more men."

Benedict's problem is that everything is exhausting and not very interesting, including foxtrot, music and dance. It's also too warm for warm foods, too moist for moist foods, and too late to go somewhere dry and cold for lunch.

"Musical therapy, it was all the rage in the seventeenth century," Clemens is saying. "That and the leeches."

"I don't really want a course of leeches either."

"Oh no, not leeches any more. Something different. Worms, sea-cucumbers. Salmon. You can't expect to самый старый город России find any power in leeches, not after they've been used for centuries."

Benedict settles on the sausages for lunch. "I'm more of a stick-with-what-you-know kind, I'm afraid."

Clemens scoffs. "No wonder you're sick of everything."

"I'm sick of the new stuff too."

"That's why you need me to cast a spell with sea-cucumbers."

Benedict doesn't quite follow this argument. "I'm not sure," he says, "there's even an argument for me to follow."

"It's not because sea cucumbers are intrinsically powerful, it's just the novelty. Listen, magic is the opposite of science." Clemens leans forward, eager to explain. "A superstition only exists because it worked, once, but the world isn't a set of buttons, press to summon attendant. It's a one-time pad, and when you've used a code then it's dead. Watch how things work, okay, see whether walking under a ladder brings you bad luck, but the most you can gain from that is a knowledge of the form of the code. Once somebody's walked under a ladder then the bad luck's theirs, and that page is torn away, and now everyone else is safe until they walk under a staircase, or over a ladder."

Benedict turns over the menu again, flipping drinks to food to drinks, considering a burger instead. "So what you're saying is that superstitions work, but in a completely untestable way."

"Once upon a time," Clemens goes on, "there was a song that stopped the rain, so now it's still there in the playgrounds, rain rain go away. It doesn't work any more, but that doesn't mean it can't help us. It shows us what the new passcode might look like. Rain, rain, please subside," and his singing voice is deep and off-key, "come back when we've gone inside." He keeps his arms on the table, leaning forward, waiting expectantly. Maybe the downpour eases off a little.

"Okay," Benedict says. "It doesn't seem to have had any actual effect, but say it did. What if someone else was singing the opposite thing at the same time?"

"Then it might not work," Clemens says. "The world won't always change just to suit you. Asking it to do something only works as long as you're willing to accept the refusal."

"So," Benedict says, and he flips over the menu again: burger, sausages, burger. "It's untestable and it only works so long as you don't mind when it doesn't. Maybe I'm missing something here, but isn't that logically equivalent to not working at all?"

"Does it matter?" Clemens takes his hat off for a moment and shakes it free of drops. "Give me a hair," he says.

"What for?"

"I'm going to make it into a new type of knot," Clemens says, "and ask the world to bring you to foxtrot lessons with me on Thursday evening."

Benedict smiles reluctantly, half charmed.