Muriel Spark is prophesied to be the most powerful witch seen in centuries of the famed Spark family. While she excels at nature magic, she sucks at the flashy skills her controlling mother Diantha values, like summoning and transmogrification. If she can't improve in those areas, Diantha won't pay for Muriel's graduate degree in herbology. Muriel prefers baking to brewing potions and gardening to casting hexes, but for the sake of her degree, she agrees to practice. When a spell to summon flour goes very wrong, though, Muriel finds herself staring down a demon--one she inadvertently summoned for a soul bargain.

Ozroth the Ruthless is a legend among demons. Cold, powerful, and merciless, he drives hard bargains to collect the emotion- and magic-filled mortal souls that power the demon plane. But his reputation has suffered ever since a bargain gone awry left Ozroth with a human soul planted in his chest--a soul that makes him emotionally unstable and no longer quite so ruthless. If he can strike a bargain with Muriel, Ozroth will earn back his deadly reputation.

But the witch is funny. And curvy. And disgustingly--endearingly--cheerful. Ozroth can't leave Muriel's side until they complete a bargain, which she refuses to do (turns out some humans are attached to their souls). Becoming awkward roommates quickly escalates when Diantha stops by and Muriel, terrified to confess to the inadvertent summoning, blurts out that she's dating the demon.

As Ozroth and Muriel struggle with their opposing goals and maintaining the appearance of a fake relationship, real attraction blooms between them. But Ozroth has a limited amount of time to strike the deal, and if Muriel gives up her soul, she'll lose all her emotions--including love.