Meet the Stinkers: Witz, Lucy, Domino, Sonny, and Loaf -- a group of clever kids who cause nothing but trouble at Dartmoor Academy's exclusive summer enrichment program. Morgan Brinway is the hapless headmaster at Dartmoor who dubbed them "The Stinkers."
The Stinkers are already on double probation when they take a school field trip to Springville Aquarium. When the Stinkers see Slappy the Sea Lion, they decide to save poor Slappy from his fate as an aquarium attraction--a -la "Free Willy". This begins a hilarious adventure... They disguise Slappy as a student and sneak him on the school bus -- then they decide to keep him in Mr. Brinway's hot tub for the night. After a lot of salt, ice, and fish'n chips, they manage to make Slappy feel at home in the hot tub. But Brinway comes home early and, through a series of mishaps, almost discovers Slappy.
After Slappy wreaks havoc at Dartmoor Parents' Day, the Stinkers decide that maybe Slappy's better off at the aquarium, after all. The students confess to Brinway, and the aquarium staff is called to retreive Slappy. But, as it turns out, Slappy isn't in good hands...
Someone takes Slappy, but it's not the people from the aquarium. The Stinkers discover that it's Anthony Boccoli, a crook who plans to sell the sea lion to the Bulgarian circus. It's now up to the Stinkers to save Slappy from a fate much worse than the aquarium. The kids devise a clever plan, and outsmart Boccoli. The Stinkers save Slappy, and Dartmoor is awarded a Presidential Commendation for the students' heroic actions. Mr. Brinway is forced to publicly commend the group he calls "The Stinkers."