Hazelthorn by CG Drews

Knives Out meets Belladonna in this gorgeously gothic queer YA horror and dark romance about an inherited estate, murderous relatives, and a garden with a taste for blood, from the New York Times bestselling author of Don't Let the Forest In and The Boy Who Steals Houses. Evander has lived like a ghost in the forgotten corners of the Hazelthorn estate ever since he was taken in by his reclusive billionaire guardian. He can never leave, he can never go in the gardens and he can never be alone with Laurie, the boy who tried to kill him seven years ago.

But when his guardian is murdered and Evander inherits Hazelthorn, Laurie may be the only one who can help him find the killer. As dark secrets unravel, moss bleeds though the walls, poisonous mushrooms flourish beneath the floorboards, and Evander must discover what he's really inherited before Hazelthorn's garden demands to be fed.