Quiet but bright Portia has just moved to a new neighborhood with her mom. Adjusting to life without a father is hard enough, but school is boring and her classmates are standoffish - and even Portia's mom is sort of distant. But things start to get better when Portia mounts a midnight excursion into the woods behind her house where she discovers a shy and sweet purple monster. Life with Jellaby is exciting, but Portia's purple friend has secrets of his own.