Harriet Wermer has made a major life change: she no longer tells lies. After a rocky start to her summer vacation, she has fully embraced her new policy of absolute honesty. What began as a dreaded trip to Marble Island has turned into a summer she never wants to end. With her mother and new baby brother finally back home from the hospital, Harriet's time at her grandmother Nanu's bed-and-breakfast is drawing to a close. She is preparing to pack her bags and say goodbye to the wonderful friends she has made. The peaceful end to her vacation is abruptly interrupted when she makes a terrible discovery. Moneypenny, Nanu's beloved and adorable basset hound, has been poisoned. Harriet knows instantly that the culprit must be one of the eccentric guests staying at the bed-and-breakfast. Teaming up with her best friend Clarence, Harriet dives headfirst into a brand new investigation. When another mysterious illness strikes the island, the stakes are raised even higher. Harriet must sharpen her sleuthing skills, practice her sneakiest spying techniques, and confront the difficult reality that the truth is sometimes much more complicated than a simple fact.