Something is wrong with Sophie.

It starts small ? a few missing seconds, a sentence she can't remember stopping. By the time her closest friends notice the gaps, the spaces are growing: lost hours, words written in her sleep, a voice in her flat that isn't hers.

They call it stress. They call it exhaustion. Eventually, they call it what it is.

When Mark finds Nicholas Grey ? calm, certain, and exactly the kind of man you'd trust with something you can't explain ? it feels like the answer they've been waiting for. Nicholas has seen this before. He knows what's inside Sophie. He knows how to get it out.

He's right about almost everything.

Don't Let Him In is a slow-burn supernatural horror about five London friends, the thing that comes for one of them, and the far more dangerous thing they let in to drive it out.

Some warnings are only understood from the other side.