While on summer vacation in the coastal town of Rubadub, four friends named Roger, Diana, Snubby, and Barney stumble upon peculiar happenings including explosions at a submarine base and eerie flashing lights during the night. Before long, the curious bunch find themselves embroiled in yet another mystery begging to be solved! In an effort to stay near his pals, Barney secretly joins a local Pierrot theatrical troupe. He soon realizes this may be his chance to finally locate his long lost actor father. But with suspicious figures lurking about town and at the old inn, who can be trusted? It appears everyone has something to hide. The foursome work together, investigating clues and connecting the dots surrounding the submarine base sabotage, stolen secrets, and a mysterious hidden identity. Can these clever children crack the case and restore order before it's too late?
 
This is book four in the series about Roger, Diana, Snubby and his dog Loony, and Barney and his monkey Miranda. Illustrated by Gilbert Dunlop.