Michael spends the summer in Wales with his Uncle Rob, Aunt Eleri, Gramps, cousin Barry, and Barry's little sister, Polly. Usually when he goes to Wales, Michael spends his time playing with fun, athletic Barry. But Barry has a broken leg, Polly wants Michael's company on the beach, and Michael's vacation turns out differently from the way he expects. One thing hasn't changed, though -- Gramps's stories. Before bed the family gathers around and listens to Gramps talk about the Sandman and his Turtles who sleep rocklike on the beach, and of Sergei Ivanovich Prokofiev, the Russian sailor who lost his ship and crew and became the lighthouse keeper on nearby Coracle Rock until he turned himself into a seagull and flew home. Polly is young enough to believe her grandfather's stories. So when she and Michael go to the beach, she fully expects the Sandman to wake up before the tide comes in -- and he does. The family doubts Polly, but when Sergei Ivanovich Prokofiev Jr. shows up with his Russian submarine and joins them for tea, the rest of them are convinced. A diverting fantasy from Morpurgo (Twist of Gold, 1993, etc.).