The Heat Stealer — Kater Cheek

First, they lose a roommate. Then they lose the air conditioner. With no money to fix it, Susan, Zoë, and Griff get desperate enough to turn to magic to keep from losing the house. Susan casts spells to solve both problems. When their new roommate's metaphysical disability magically keeps the house cooler, everyone thinks they've gotten lucky. And then everyone stops sleeping. Susan discovers the new girl has a dark trail of accidental deaths in her past; nearly everyone who has lived with her has gone insane or died. But even after Griff and Zoë suffer horrible accidents, no one believes Susan's theory that the new roommate is to blame. Susan decides to find a way to cure her new roommate's disability before she loses everyone she cares about.