Timmy and Lassie aid a mallard duck who laid her eggs on the track of a soon-to-be-opened spur line.

A boy restless with his rural life and chafing under the ""no trespassing"" signs of their territorial neighbor wishes to strike out to ""follow his star""--stealing the neighbor's mare to do so.

Ron and Dale return to the Holden Ranch, where Lassie is welcomed by Garth Holden and his foster sons, boys who have been orphaned or abandoned by their families.

Garth's brother Keith is met with resentment when he takes over running the ranch, but he proves his mettle when a storm strikes the ranch and starts a fire that traps Lassie in the woods.

Joey runs away when he finds out he has to leave the ranch.