11-year-old Sesame Seade, Cambridge's number-one supersleuth, knows that mysteries turn up in unexpected places. But in her third adventure, even unflappable Sesame is surprised to discover a locked treasure chest nestled along the bank of the River Cam. She's certain it belongs to pirates, but before she can investigate, another mystery floats her way: several Cambridge University rowing team members are coming down with a terrible stomach bug—and with the world-famous Boat Race between Oxford and Cambridge looming, Sesame suspects foul play. Could the treasure chest have something to do with their illness? It's going to take a kidnapping and a high-speed motorboat chase for Sesame to save the day again!