Maren’s grandmother left her two things: a house full of mirrors and a horror she can’t escape.

When sixteen-year-old Maren moves into her dead grandmother’s estate, she thinks the hardest part will be watching her mother fade away from depression.

But the house has thirty-two mirrors, and they’re not just reflecting anymore. Her reflection moves when she doesn’t. Writes messages. Talks to things that aren’t there.

And something is hunting from the other side of the glass. The journals hidden in her grandmother’s desk reveal a terrible truth: in 1952, desperate to escape an abusive marriage, Iris made a trade with the mirror in the basement.

She swapped places with her own reflection—and created a wound in reality. A seam between worlds that attracts predators. The thing her grandmother called the Hollow-Walker has been feeding on their family for generations. It consumed Iris’s reflection. It was fed half of Maren’s mother as a baby—which is why Mom has always been so fragile, so disconnected, caught between two worlds.

Now it wants Maren. But Maren’s reflection—the girl trapped in the mirror-world—knows a way to stop it. A binding ritual that will seal the Hollow-Walker away forever and make Maren’s mother whole again.

All it requires is a willing sacrifice. One girl must cross into the mirror-world and become the seal. Trap the monster by trapping herself. Fill the gap by staying in it. Forever.

Maren has spent her whole life disappearing—making herself smaller, invisible, responsible for everyone else.

Now she must choose: fade away slowly in a life where she doesn’t matter, or sacrifice everything to save the person she loves most.

Some choices close doors. Others become them.