“We need light!” It was Will, having returned to the entryway; he had Aunt Tessa with him, and they were both in gear. He was snapping out orders—everyone who could not join the battle was to fetch a witchlight rune-stone and head to an open window to direct the light down onto those fighting outside.

Thomas exchanged a quick glance with the others. He had no intention of being kept back so he could stand at a window with a witchlight. If the Institute was being attacked, he wanted to be out there, defending it.

It was Alastair who moved first. He started down the steps, Christopher and Thomas on his heels. Thomas coughed as the air thickened around them, suffused with the rank, damp smell of salt, fish, and rotting seaweed. As they reached the bottom of the steps, Thomas’s boots came down in freezing water. He could hear Christopher exclaiming about scientific impossibilities.

“Well, it might be impossible,” said Alastair, rather reasonably, “but it’s happening.”

“Whatever it is,” Thomas said. The courtyard began to brighten—dozens of windows around the Institute were being flung open. Thomas recognized some of the faces there, hands holding out glowing rune-stones—there was Aunt Cecily, and Mrs. Bridgestock, Piers Wentworth, and several of the Pouncebys.

In the increasing light, Thomas could see that the entire courtyard was afroth with ocean, gunmetal-gray, sloshing chaotically back and forth as though caught in a windstorm. Shadowhunters had clambered atop heaps of piled flagstones and other rubble, hacking and slashing at the things emerging from the water. They were long, like sea serpents—a muddy shade somewhere between brown, gray, and green, but shining slickly as though metallic. One whipped through the air toward Anna; she flicked her whip, slicing it in half. The stump thrashed, spraying gray-green, watery ichor. Thomas heard Eugenia shout—he hadn’t realized she was in the courtyard—and he spun, catching sight of the remains of the tentacle wrapping itself around Augustus Pounceby’s waist.

Augustus screamed, dropping his seraph blade, and clutched desperately at the fleshy green appendage tightening around his body. It was clearly choking the breath out of him; his face had gone red and he was gasping for air. Thomas started forward, but Eugenia was already there, her longsword flashing. She brought it down at an angle, slicing through Augustus’s gear jacket and then through the tentacle itself. It fell away in two spasming chunks and Augustus sank to his knees, clutching his midsection.

“Eugenia,” he wheezed. “Please—I don’t deserve—”

Eugenia shot him a disgusted look. “No, you don’t,” she said. “Now pick up your weapon and make yourself useful, for once.”

She strode off, returning to the thick of the battle, pausing only to wink at Thomas as she hurried by.

“That was unexpectedly satisfying,” said Christopher.