In their second adventure, the guinea pigs face a new mystery that will take them to the depths of the sewers, where the thugs and legendary beasts take refuge. It all starts with the discovery of an old map of the city's sewer system. The always restless Broccoli convinces her friends to go on a reconnaissance mission and find out if any of the stories told about the sewers are true. Like that of Worm, a terrible monster that lives in the depths and is always hungry. Or perhaps that of a fabulous treasure that was lost more than fifty years ago. As they go through the tunnels, a gigantic wave drags them to an unknown area. They are in danger and there is no way out… Will they be able to escape? Will they meet Worm, and will he devour them?