Harriet Wermer is absolutely, positively thrilled to be spending her entire summer vacation far away from her parents and the meticulously planned schedule she had been looking forward to all year. Alright, so maybe she is not telling the complete truth. Lying is something Harriet occasionally struggles with, alongside her intense frustration that her father shipped her off to Marble Island without asking for her opinion. Now, she is stuck at her grandmother Nanu's cozy bed-and-breakfast, accompanied only by her perfect cat, Matzo Ball, and Nanu's droopy old basset hound, Moneypenny. Despite her initial resentment, Harriet quickly realizes that the small California island is not the boring exile she expected. The quirky bed-and-breakfast is filled with unusual guests and endless nooks to explore. The real excitement begins when she accidentally uncovers a genuine mystery deeply connected to her father's own childhood spent on the island. Armed with her sharp wit and a burning curiosity, Harriet decides that getting to the bottom of this decades-old secret is the perfect way to spend her summer. She is going to solve the case, uncover the facts about her dad, and have a real adventure. And that is the honest truth.