When Claude Monet's "Beach in Pourville" disappears from the National Museum in Poznan, and Julka's aunt is falsely accused of theft, Julka and her friend Olek must find the painting.

In Poznan (Posen), local schoolboy Olek and his classmates Felka and Julka Strzalkowska attend the unveiling by the latter's aunt, director of the city's national art museum, of Poland's only Monet "Beach in Pourville", which was stolen there 20 years ago. Only now it's destroyed by an explosion, but found a forgery, painted and sold by Felka's artist mother Kaja. While haughty police detective inspector Rafalski arrest both women for questioning and orders searches by loyal constable Novak, brilliant young deputy director Karol, who practically runs the museum, helps the kids, who initially commandeer him as driver, to prove their innocence by finding culprit and original painting. That turns out complex and dangerous.—KGF Vissers