15 in the Danny Dunn Series. "Castaways! "I challenge you to a duel of deserts islands!" Dr. Grimes cries, when Professor Bullfinch accuses him of not being practical. He plans to go ashore on an uninhabited desert island, and Professor on another. After a month they will see who has survived the best! Danny and Joe soon get permission to join them and the four take off in the scientists' private plane. But they crash-land in the ocean and are REALLY marooned on an island -- off the coast of Peru! Danny has so much fun that he wants to stay, and "breaks" their short-wave radio so they can't signal for help. Then he finds the long arrow embedded in the tree -- a terrifying clue that someone else is on the island . . .