The film starts with the understanding that the makers of the Benji films are going to various towns in the U.S. looking for the next dog to play Benji. In a small Mississippi town, a freelance dog breeder named Hatchett keeps a backyard kennel under poor conditions behind his home. He lives with a young boy named Colby and his mother and is verbally abusive to them, but Colby loves dogs and secretly nurtures a female black dog who is Hatchett's top breeder. He goes to an abandoned house in the neighborhood and takes food and water to the black dog so she can produce milk for her new pups. Hatchett learns of this and takes the black puppies but abandons a fluffy, light-colored "mongrel". Over several months, Colby secretly cares for the puppy, and she grows into the unnamed fluffy dog that will become Benji.
Meanwhile, two Animal Control officers named Livingston and Sheldon come across a shaggy dog that is impossible to catch. A local elderly man, Zachariah Finch, offers food to the stray at his home in the woods and becomes attached to him. The dog is dubbed "Lizard Tongue" by the officers looking for him (due to its long tongue always hanging out of its mouth). When the fluffy dog sees that her mother is sick in the kennel, she opens her cage and helps her escape. Then she gets Lizard Tongue to help when she is too weak to eat, and they both draw the Animal Control officers to the abandoned house and the ailing black mother dog. At the shelter, a veterinarian determines she is dying from over-breeding and poor care, so the shelter director and the local sheriff authorize the vet to spay the dog.
When Hatchett learns that the Benji film producer is in town and wants the fluffy dog to be the new Benji, he intimidates Colby into lying about being the owner. At the shelter, the fluffy dog is reunited with her mother, and Colby tells everyone the truth about the dog, which makes Hatchett lose his temper and get arrested. The end credits show various scenes from the film as they were shot and make reference to the origins of the shelter dogs used in the film.
Benji: Off the Leash! was filmed in various parts of Utah such as Kaysville, Ogden, Payson and Salt Lake City as were stated in the end credits. The credits also jokingly refer to the number of computer-generated imagery effects and animatronic dogs used in the film as "none".
On Rotten Tomatoes, the film received a score of 33%, based on 43 reviews, with an average score of 4.3/10.
Nick Whitaker as Colby, the son of Hatchett and his wife
Chris Kendrick as Terrance Muncy Hatchett, a cruel and arrogant dog breeder
Christy Summerhays as Colby's mother
Neal Barth as Zachariah Finch, a local elderly man
Randall Newsome as Livingston, an animal control officer
Duane Stephens as Sheldon, an animal control officer
Nate Bynum as Sgt. Oswald Lewis
Melinda Haynes as Animal Shelter Director
Joey Miyashima as Veterinarian
Scott Wilkenson as Film Producer
Jeff Olson as Paul's Market owner
Moochie (credited as "Benji") as Benji, a white fluffy dog
Sally Sue as 8-Week-Old Benji
Odola as 4-Month-Old Benji
Shaggy as Lizard Tongue, a long-tongued shaggy dog