From the New York Times bestselling author of the Emily Windsnap series comes a captivating adventure about family, friendship, and the bonds that bridge time. The sleepy seaside village of Porthaven hides a mystery: Mia's grandad has vanished, and nobody knows why. When Mia and her mom rush to Porthaven to help her grandmother, Mia imagines long dreary days with no one to talk to except for the old-time fisherman at her grandparents' pub. But that's before Mia finds a diary on an empty, docked fishing boat and starts exchanging notes with a local girl named Dee, a girl who seems much like her. Mia is excited about having a new friend, but why do their plans to meet each other never materialize? And why does Dee claim to be stuck at home due to violent storms when Mia sees only sunny skies? Will Mia be able to solve the mystery of where—and when—her grandfather and friend might be before time and tide forever wash away their futures?