Detective Callum Myles has seen a lot of strange things in his career. But when a string of victims are found carefully posed in their own apartments—each one marked by an identical rabbit figurine and an impossible signature—he's pulled into a case that defies reason and rewrites memory.

All the evidence points toward one man: Gideon Vale, a watchmaker with a precise alibi and no apparent motive. But there's a problem—the apartment where the murders began doesn't exist. Unit 6B was never built. It doesn't appear on blueprints. Yet it's always there... waiting.

As Myles unravels the layers of an invisible apartment and a killer who doesn't officially exist, he's forced to confront secrets buried in both the city's foundations and his own fractured past. Meanwhile, Gideon begins to question not just what he's forgotten, but who he truly is—and what's been living inside him all along.

Reality begins to slip. The walls shift. And in the hollow space between fact and memory, something is keeping score.

How do you catch a killer who lives where no one lives at all?