Mara's in hell! Neither one of the guys in her life is talking to her. Paul, her ex-boyfriend, is afraid she's going to give birth to a baby demon—complete with horns and hooves. He wants proof that he's actually the father. And her best friend, Gus, is so obsessed with his new boyfriend and his plans for the late, great, Lord Grundleshanks the Poisonous Toad, he has no time for anyone else.

After Gus flips the seasons and manages to bring summer into winter, everything starts going weirdly wrong. Summer refuses to leave. Household electronics start going haywire. When J.J., a local boy, vanishes from Mara's car, Mara begins to suspect he's been turned into a rat. But it's such a crazy idea, who could she possibly talk to abut it? Then, her dead Aunt Tillie shows up to warn her that Gus is in trouble—big trouble—and it's up to Mara to save him.

Before Mara can stop him, Gus opens up a portal to Hell and the Devil comes calling. Now, she's got her hands full, trying to find out what happened to J.J., assure Paul she's not going to give birth to a mythological creature, and broker a truce between Gus and the Devil before Gus becomes Hell's newest resident.