That night, the Mermaid’s hydrophones recorded a single sound from the deep: the Bismarck’s ship’s bell, ringing once. No one had touched it. No current could reach it.

Lena activated the robotic arm, a delicate claw carrying a titanium wreath. She maneuvered it toward the gun barrel. The Bismarck’s steel was not smooth. It was draped in rusticles—orange-brown icicles of oxidized metal, each one a colony of bacteria. They swayed in the sub’s wake like seaweed on a dead tree.

Then the Bismarck groaned. A new sound: not a growl, but a sigh. The ship settled two inches into the seabed. A cloud of silt rose around her, and in that cloud, Lena swore she saw shapes—men, hundreds of them, standing at attention on an inverted deck.