The apartment was affordable. Convenient. Perfect.

Until Alex noticed their reflection moving a fraction of a second too late.

At first, the wrongness is subtle. A coffee maker that turns itself on. Windows that appear on the wrong wall. Door numbers that flicker between 3B and 8B when you're not looking directly at them. Alex tells themselves it's stress, exhaustion, the aftermath of a bad breakup.

But then the mirrors start showing someone else. Someone who looks exactly like Alex. Someone who's learning how to be them.

The building super, Delgado, has seen this before. Forty-three tenants over thirty-eight years. All of them disappeared. All of them replaced by something that wasn't quite human. He gives Alex a key to a storage locker and a warning: Don't let your double touch you.

Because Apartment 3B isn't just an apartment. It's a threshold between dimensions. A collection point for people who fall through the cracks in reality. And once the apartment starts the replacement process, there's no way out.

Unless Alex can do what no one else has managed: escape before the swap is complete.

But the apartment is patient. The apartment is eternal. And the apartment always wins.

For fans of Blake Crouch's Dark Matter, Paul Tremblay's psychological horror, and the dimensional dread of Annihilation, Apartment 3B is a mind-bending psychological thriller about identity, reality, and the terrifying question: how do you prove you're the real you?