Chance, a white and brindle bulldog, tells the story of how he was abandoned as a puppy and lived on the street until the pound picked him up and put him behind bars. He explains that he had a second chance in life when the Seaver family adopted him. Sassy, the Seaver’s cream-colored Himalayan cat, interrupts Chance as he chews a dress inside a suitcase. Sassy is upset because she was awakened by Chance’s noisy snarls. Downstairs in the garden, Bob Seaver and Laura Burnford are getting married with Laura’s three children, Peter, Hope and Jamie, at their side. Chance describes how each child belongs to a different animal companion; Peter is in the care of Shadow, an old and wise Golden Retriever, Hope belongs to Sassy, and Jamie, the youngest son, is Chance’s mischievous cohort. As Chance and Sassy exchange playful insults, Chance chases Sassy and their commotion interrupts the wedding party as Bob and Laura are pronounced husband and wife. At the reception, Chance jockeys for table scraps while Shadow, an obedient and faithful dog, tries to keep Chance from eating the humans’ food. Chance begs for a handout from two ladies who discuss the future of the new couple and their children and mention that the family will be temporarily moving to San Francisco for Bob’s work. The pets will be left with a friend while they are away. Later, at Kate’s ranch, Peter, Hope and Jamie bid a sorrowful farewell to their animals. Although Chance has fun chasing farm animals and assumes, from past experience, that their owners have left for good, Shadow maintains more faith in humans and knows that his bond with Peter will be restored. When Kate leaves on a stock drive to deliver her horses to winter grazing fields, the animals become discouraged and Shadow decides it has been too long since he has seen Peter. He jumps the fence and runs into the woods to find his way home while Sassy and Chance follow. The group makes it to the top of a mountain, thinking that home is just on the other side, but they see nothing but more mountains and woodlands. A determined Shadow pushes them to keep traveling, fearing that Peter might be in trouble. After a frightening night in the wild, Shadow leads the others to a river where Sassy catches fish for breakfast. As Chance’s fish flops on the ground, it leads him to a couple of bear cubs. Chance proudly chases the cubs off, but when the mother bear defends her young, the animals are scared away. Shadow decides they need to cross the river but Sassy does not want to get wet. When Sassy crosses the river on rocks and tree trunks, one of the logs breaks and she is swept away by the current. Shadow swims after her, but Sassy disappears over a waterfall. Although Shadow and Chance search for her, they are forced to give up and Shadow regrets that he failed in his responsibility to love and protect his companion. He explains to Chance that this is the noble role of their species. Not far away, a man watching a bald eagle finds Sassy, barely alive, washed up next to the river and nurses her back to health. Starving, Chance unsuccessfully hunts for food while Shadow attempts to teach him the importance of patience. In the meantime, Kate returns to her ranch and realizes that Shadow, Chance, and Sassy have run away. The Seaver children are devastated by the news and Peter yells at his stepfather for leaving the animals behind. Feeling remorseful that he has let his new family down, Bob creates a poster to be dispersed across the country with an image of the animals announcing: “Lost Pets – Reward.” Back in the woods, Shadow and Chance try to catch food, but while Shadow is face deep in the river, Chance sees a mountain lion and they run for their lives. Facing a dead end in their escape route at the edge a cliff, Shadow ingeniously lures the mountain lion onto a log balanced on a rock and Chance jumps on the other end, catapulting the mountain lion over the cliff and into the river below. Sassy hears Shadow and Chance’s celebratory barking in the distance and leaves her new companion to reunite with the dogs. The trio goes fishing again and, with Sassy’s help, they are finally able to eat. Despite Shadow’s warning, Chance playfully examines a porcupine and gets wounded with spines from its tail. Back in San Francisco, Peter attempts to file a missing person police report for the animals, and the officer suggests that he make a poster instead. When he returns home, Peter finds that his stepfather has already made a poster, and he regains faith in Bob. As the animals continue their journey, Shadow hears crying and finds a lost girl. Shadow, Sassy, and Chance stay with her through the night. In the morning, Shadow hears a search party calling the girl’s name and leads them to her. Forest Service personnel from the search party recognize the animals from Bob’s poster and take them to the Pineville Animal Shelter. Informed that their pets have been found, the Seaver children leave school and the family heads out to meet them with great excitement. Upon arriving at the shelter, Chance becomes anxious because he is reminded of his past experiences and, as the two dogs are restrained, Sassy escapes. While the shelter vet pulls porcupine spines from Chance’s snout, Sassy sneaks into the shelter and releases Shadow. Hearing Chance’s moans, Shadow fears that his friend is being killed and Sassy distracts a shelter worker so Shadow can help Chance break free. The dogs dig a hole under the fence and the animals narrowly escape into the woods just as the Seaver family drives into the shelter. Although Shadow gets a gut feeling that they should return to Pineville, the animals continue on their journey home. Shadow, Sassy, and Chance finally reach the top of the last mountain and see their hometown below. As they make the last leg of their adventure, they traverse a train yard, jumping tracks and precariously darting in front of oncoming trains. While Shadow steps across a path of wooden boards, they break beneath him and he plunges into a mud pit. Encouraged by his companions, Shadow struggles to climb out, but he has injured his leg and wants to give up. Despite Chance’s desperate call to action, Shadow says he is too old to make it and advises Chance to stand on his own. Chance tells Shadow he loves him and that he won’t let him give up. Meanwhile, the Seaver family has returned home. As Bob plays basketball with the kids, he is surprised to hear them call him “Daddy” for the first time. They hear barking in the distance and Chance bounds over the hill, tackling Jamie. Soon, Sassy runs to Hope. The family waits for Shadow, but he is nowhere to be seen. Just when Peter is about to lose faith, Shadow limps over the hill, regains his strength, and runs into the boy’s arms. As the family goes into the house, Chance reflects on the lessons of sacrifice, friendship and love he learned on his journey. Once inside, however, he is unable to restrain his enthusiasm for the Thanksgiving turkey.