The world's most famouse painting is hiding a big secret! An X-ray of the Mona Mousa reveals a strange riddle. Solving the clues takes Geronimo to the most dangerous parts of the city, but facing the hair-raising rollercoasters and vicious octopuses is all worth it for the amazing treasure at the end of the trail. Isn't it? The series is perfect for 5 to 8 year old's both avid and reluctant readers due to its expressive typeset, fun illustrations and humorous stories.