While Corey is at Cape Kennedy participating in a paracute-testing project, Lassie encounters Atlas, a guard dog gone wild after the death of his master.

Still in Florida, Corey and Lassie befriend Donnie Baker, whose puppy was run over while chasing a rabbit, and must rescue Atlas, trapped in the swamp.

Lassie has her hands full: she's reacclimating Atlas to society while keeping watch over a bald eagle injured during one of the parachute tests.