Uncle Steve is shot by an over-eager hunter and Lassie is impounded for attacking the hunter. Now Will must rescue his canine friend and Lassie must get help for the unconscious Steve.
After accidentally getting locked in the back of a truck, Lassie finds herself lost in the city and must find her way home, befriending a runaway along the way.
Megan and her friend mysteriously become sick after skinny-dipping in a stream. Chris, Will and Lassie do some investigating and learn that the cause may be linked to illegal chemical dumping.
Chris and Dee McCullogh are upset the police officer is handing out fliers stating Halloween is dangerous and that children should remain at home, so they decide to conduct an old fashioned Halloween with all the block parents supervising.
A miniature horse that Will is temporarily taking care of becomes the source of contention between the McCulloughs and a neighbor who's a local politician.