A man pursuing wolf bounty shoots a wolf in protected territory and then watches Erickson and Turner nurse the wolf back to health with help from Lassie who uses the creature's paternal instinct to gain recovery.
When Allan surveys an old Air Force bombing range to develop as a grassland, his helper, who is partially buried by a landslide, dislodges an old unexploded bomb which Allan must disarm via remote instructions from the ranger station.
Lassie attempts to rescue a fawn that has become trapped in a vinyl reservoir that is part of an experimental water system constructed to rescue the cattle business of a lady rancher that leases from the forest service.
Scott, with Lassie, joins Park Ranger Ivan in flying over Superstition Canyon discussing local legends. They locate a hardy prospector Hobart who has appendicitis. Lassie is left to take care of his burro Emily until Scott can return.
Scott and Lassie visit San Francisco's Chinatown. When Lassie is struck by a car while saving a child, she is taken to a vet's office. She may have amnesia so when a fire breaks out in the office, she escapes with no idea where she is or where she should go.
The next day Lassie searches for her identity. She visits a wax museum at Fisherman's Wharf and the waterfront, where she meets a down-on-his-luck young fisherman with a family and a boat loan he can't repay.
Lassie heads back into San Francisco over the Golden Gate Bridge and meets Sue, a lonely runaway. Next day Lassie brings together Sue with a lonely soldier. On her own again, Lassie is mistaken for a possibly-rabid collie named Tawny.
Her memory now recovering, Lassie flees through San Francisco streets while being hunted by both health officials and police as a rabid dog. Meanwhile Bob joins Scott in the search for their beloved collie.
Bob takes Lassie and Neeka, an Alaskan native, to see the cliff dwellings at Mesa Verde Park. While exploring Neeka falls, breaking his leg with Lassie going for help. A daring and dangerous rescue is conducted by the rangers.
Clint and Edie, along with Clint's guide dog Ginger, live in a remote area of the forest. Bob leaves Lassie for a visit so when Edie is injured Lassie leads Clint to her. Lassie goes for help while Ginger faces a mountain lion.
On a trip to survey tribal lands Lassie, Bob and a Navajo guide find and rescue a dog swimming in Lake Powell. Chuka is a lazy dog and would rather rest than tend sheep, but things change quickly when his owner is injured and Lassie must go for help.