A blue-masked gang is trying to destroy Gill park. Everything--fountains, trees, statues--has been spray painted blue. Having returned to Gill Park to attend the Gill Park Gallery School, Willy Wilson finds himself caught up in the struggle to save his park. But the blue-masked gang isn't the only mystery demanding Willy's efforts. The parks former owner, the eccentric millionaire Otto Pettingill, has left his own mystery for Willy to solve, this one leading to treasure. Will Willy be able to solve Otto's clues, defend his park, and succeed in his demanding new school?