I don't even know if 'twist' is a strong enough word for that ending. It's more like the book took the entire floor out from under me. The whole setup with Louise getting involved with David, her boss, and befriending his wife Adele, it felt like a standard love triangle thriller for a while. Then you get Adele's journals hinting at astral projection, and it just seems like this weird, maybe symbolic, maybe supernatural layer. But the real gut-punch is that Adele isn't in her own body anymore.
Years before, the real Adele died in a fire at the mental institution. Her friend, Rob, a fellow patient she taught to 'astral project,' swapped bodies with her as she was dying, leaving his own sick body behind. So the 'Adele' we've been following is actually Rob, living her life, married to David. David knows something is off, but not the truth. And Louise? She learns the projection trick from Adele/Rob and tries to use it to spy, but gets her consciousness trapped and swapped out. The final scene is David living with 'Louise,' who is now actually Rob-in-Louise's-body, having successfully performed the swap a second time. It's a permanent, horrifying theft of identity that reframes every single interaction in the book. It’s not just a clever plot turn; it’s deeply unsettling because the person you’ve been rooting for is just… gone, replaced by a manipulative predator. The horror lingers because there’s no victory, just a perfect, undetected crime.