Captain Flatus Codswallup needs ten-year-old Lucas's help getting his sewer-sailing ship seaworthy, and flushes him as a new recruit. Lucas learns it's not all toots and giggles as a pirate in the sewer when threats of mutiny strike. Lucas must decide between saving Flatus's butt and getting home before his plumber father misses him. But when the pirate ship falls under attack, Lucas learns who Flatus's sworn enemies are. Plumbers like Dad! Now Lucas has to choose a side that doesn't get everybody killed as plumbers and pirates meet in the messiest battle the sewers have ever seen.