But of course she was right: it would be cool to be a blue whale. The idea grew on him. There was no particular reason to do it, other than it would be more interesting, but that seemed like enough. What else was magic for? It was safe: they were legally protected, and barring scattered orca attacks blue whales had no natural predators. The only downside was that even though they were fast swimmers by cetacean standards they turned out to be painfully slow compared with most birds, let alone the great snipe—20 mph was about a blue whale’s top speed, at least over long distances. At that rate it would take them a couple of months to get to Antarctica.

“I doubt we could delay the job that long,” Quentin said.

“Yeah,” Plum said sadly. “It would have been nice though. Oh well, another dream dies.”

But in the end they found a way to save it. They flew commercial most of the way, as far as Ushuaia, a small but unexpectedly charming port in Tierra del Fuego that claimed the distinction of being the southernmost city in the world. It was squeezed into a narrow strip of land between the Beagle Channel and the snow-covered peaks of the Martial Range behind it, as if it were backed up against them and trying not to fall into the freezing water. From there they could cross the Drake Passage to the coast of Antarctica in the form of blue whales.

From the airport they took a taxi to the waterfront. They’d brought no luggage. From the safety of a concrete wharf, the Beagle Channel did indeed look forbiddingly cold, a flat gray stripe of sea lapped at by glaciers on either side. But they couldn’t do anything from dry land. For the actual transformation they’d have to be in deep water.

Chartering a boat would have been the sensible thing to do, if they were tourists, or sport fishermen, or smugglers. But Quentin and Plum were magicians, so they waited until midnight, then cast spells on their shoes and hiked out onto the channel on foot.

It was tricky at first, till they made it out through the mercifully light surf and got used to the rhythm of the swells. It was only their shoes that were buoyant, so if they fell over they’d get wet like anybody else. Once they were a couple hundred yards from shore, out beyond the glow of the lights along the beach, it got quiet and very dark and very cold.

“I feel vaguely blasphemous doing this,” Plum said. “Like, only Jesus is allowed to do this.”

“I really don’t think he’d mind.”

“How do you know what Jesus would mind?” She was silent for a minute, concentrating on the walking. It was not wholly unlike trying to walk on a black, cold, unusually violent bouncy castle. “Did you like Brakebills South?”