The G-man's son at Porpoise Island

"The G-man's Son at Porpoise Island" by Warren F. Robinson is an adventure story centering on Stanley Sandborn, whose father is a G-man, and his friend John Tallman, when sailing plans turn treacherous after arriving at a mysterious island. Beginning with a camping trip by boat which is quickly derailed by a mysterious speedboat and a collision with something hidden under the surface of the water near Black Cove, the boys find themselves caught up in a dangerous plot, encountering odd lights, suspicious sounds, and the enigmatic Mr. Nevens. What started as a vacation suddenly becomes the fight of their lives as Stanley and John uncover criminal activity hiding on Porpoise Island.