A four-hundred-year-old crawling prison that drags across Earth's ocean floor, caging the Republic's worst war criminals.
Deepgrave is an ancient prison that has crawled the abyssal plains of Earth's oceans for four hundred years—a crab-like station whose ribbed dome rides on a legion of barnacled hydraulic legs, sucking up refuse through belly-umbilicals and, in its guts, the sinners of first the Society and now the Republic. Once it held murderers, rapists, and political prisoners; since Mustang abolished the Republic's death penalty (the day she pulled the Jackal's feet), it holds the war criminals Darrow would rather have hanged—Boneriders and worse—in the solitary-confinement cells of its high-security Omega Level, where prisoners never see a face or hear a voice. Its lethal external defenses guard against assault, but its interior was built to keep people in, not out.
Manned largely by loyal Martian Grays and Vox Populi political officers, and reformed only in its cruelty (Caraval has blocked prison reform for years), Deepgrave is 'escaped' by no one in history—save, rumor holds, Sevro's father Fitchner. Darrow's Howlers drill in through the desalination plant to free a war criminal from cell O-2983, only to find it empty.
A humped, crab-like undersea station: a dome ribbed with intake vents, docking stations, and antennae atop barnacle-covered hydraulic legs that thump across the abyssal sand, trailing umbilical tubes; inside, rusted ancient blast-doors and cold, keyless solitary cells.
The setting of the Howlers' undersea raid; the Republic's abyssal prison for war criminals and the vault Darrow means to crack.