Poppy is six, alone, and bullied by every kid in town. Her parents died saving strangers, and she lives by herself in a broken-down shack. On Christmas Eve she writes a wish letter, but a spelling slip sends it to Satan instead of Santa.
Satan answers by sending Cerberus, disguised as a one-headed puppy with a red bow, under strict orders to keep her safe. Poppy names him Pippy and realizes the puppy can actually speak to her. Satan keeps checking in, and when the bullying goes too far he steps in himself, breaking the laws of Hell and paying for it. Then the orphanage comes to take Poppy away.