The Lattice Below Halcyon Nine

Nine hundred meters down the wall of the Kestrel Trench, the research colony Halcyon Nine shelters 140 people beneath a steel dome that groans like a whale. Noor Halvorsen, 27, is its hull listener, a pressure-acoustics technician who sleeps in headphones and can name every rivet by its creak. One night she hears a new sound outside the dome. Something clicks back at her sonar pings, repeating each pattern in reverse. Floodlights then reveal a pale mineral lattice on the trench wall, grown overnight into an exact copy of the colony's floor plan. Noor believes it is a living intelligence learning them. Chief geologist Ezra Mbeki-Strand, 48, reads the same data as crystal growth fed by a methane pocket, one that could collapse the slope within weeks. He wants to evacuate quietly before the funding consortium's mining crew arrives to harvest the lattice. Noor wants proof that it thinks before anyone leaves. Neither can reach the deep sensor array alone. She holds the acoustic keys, and he holds the dive clearance. So they start lying together, forging maintenance logs, rationing the oxygen on stolen dives and deceiving the colonists who trust them. Then the lattice grows a new shape. It is the outline of a diver whose death, three years ago, Ezra signed off as an accident.