Pirates, Prowlers, and Cherry Pie by Susan Brown

Fiona Smith is in summer exile at her horrible Aunt Irene's house. Bullied and beleaguered by her snobby cousins, Fiona quickly realizes there is more wrong in the beachside home than miserable tempers. Someone is systematically robbing all the wealthy houses along the shore. Despite her plan for revenge on her nasty cousins, Fiona is lured into the mystery when an innocent boy is accused of the crime.

Between pirate maps, creepy prowlers, and splattered cherry pie, Fiona is determined to solve the mystery, win the reward, and make this into the best summer ever!