Flesh and Blood — Patti Larsen

When Syd's father chooses to use blood magic in an attempt to return to Demonicon, he not only seals his own fate, a death sentence, he somehow transfers all of his remaining power into the demon cat, Sassafras. Transformed by Harry's magic, Sassafras is suddenly back to his human form. Faced with a sullen and angry teen demon who refuses to help, Syd must somehow find a way to reach the other plane before Harry's depleted body destroys itself or he is burned at the stake for his crime.