Tom's unsuccessful rocket test launches a wild chain of events, that leads a group of friends — Tom, Harri, and Perch — into a complicated mystery, as a greedy gang of criminals sets its sights on an old, valuable painting. The boys find themselves in a thrilling adventure, where they always manage to stay one step ahead of both the adults and the criminals — though only barely.

Unexpected turns, humorous incidents, and the warmth of friendship keeps the story fun and light-hearted, even as danger constantly lurks in the background. Tom, Harri and Perch must depend on their cleverness and courage, as one wrong step could expose them to the criminals.