Peter's cat, Shadow, had been a birthday present from his mom. She had said he was old enough to be responsible for a pet. But now Shadow had disappeared. Peter knew it was up to him to find her. He begins his search in the neighborhood on the island where he lives. He puts up posters and asks the summer residents if they have seen his cat, but Shadow is not found. Peter realizes that his cat may not be in the neighborhood, but somewhere else on the island. Clues eventually convince Peter that Shadow is not on the island anymore, but on the mainland. He tells his ideas to his neighbor, Mr. Mullins. Mr. Mullins praises Peter for his detective work and offers to take him across the long bridge to the mainland. Is Shadow found where Peter thought she would be? Well, not exactly. Readers will love the happy, surprise ending!