Mark, Nora and Toby Brice are well under way in their cabin sloop on their voyage from Kewanaka Bay on Long Island Sound to Maine, when they find a stowaway on board. Nora quickly spots the fourteen year old boy's identity. He is orphaned Pierre Langdon, who has stowed away to try to reach Aunt Esther on Lone Island in Maine, and to escape half-mad Mr. Coyle, executor of his grandparents' estate. Adolescence is convincingly described; suspense rides high in solving the mystery of Mr. Coyle's delusions about Pierre; tension mounts as the Brice children help him to reach Lone Island; dialogue has verisimilitude and the background of salty seaports, Kennebunkport, Plymouth, Kittery and Casco Bay conveys the brisk air of the New England coastline. All in all, an exceptionally shipshape nautical mystery for teen agers.