Tom and his friends are excited to be spending their spring break out at Lake Carlopa, where they'll be camping and testing inventions to clean up the shores as part of a service project sponsored by Swift Enterprises. Rock star of the engineering world Jonathan J. Jefferson is even set to make an appearance as part of the event. Tom's also really looking forward to using the trip as an opportunity to test out his most ambitious creation yet--a two-man submarine! Lake Carlopa is a haven for scuba divers because of its clear waters, and it will be the perfect place for the sub's maiden voyage.

But when a scuba diving team shows up at the campsite and seems to be there for more than just pleasure diving, Tom and his friends wonder what they're really up to. Are the divers using the exhibition as cover for something more sinister?