As darkness blankets the Ontario wilderness, bachelor John Longridge prepares for an upcoming hunting trip. Prior to his departure, he thoughtfully writes a note for his housekeeper, Mrs. Oakes, detailing his intentions and mentioning that he will allow Tao, the Siamese cat, and Luath, the Yellow Labrador, along with Bodger, the elderly English Bull Terrier, to roam free in the morning. After completing this task, he retires for the night, pondering the recent opportunity presented by his friend John Hunter for a visiting fellowship at the University of Oxford. This revelation inspires him to take care of not just Luath, but also Tao and Bodger, who belong to Hunter's children, Elizabeth and Peter.
The day dawns, and Longridge releases the trio into his yard before departing, unaware of the adventures awaiting them. When Mrs. Oakes and her husband Bert arrive, they mistakenly believe that Longridge has taken the animals along. Meanwhile, driven by the call of wild geese, Luath sneaks out, leading Tao and Bodger to embark westward, clueless about the distance they need to cover.
As they journey on, it becomes clear that Bodger's age hinders their progress. With no human aid to rely upon for food, the trio faces mounting challenges. Days pass, and Bodger collapses from fatigue, prompting Tao to hunt for birds while Luath seeks water.
In a twist of fate, Bodger encounters two playful American black bear cubs. His exhausted state fails to alarm them, leading to a playful scuffle that soon attracts the attention of their protective mother. Luckily, Tao and Luath return just in time to scare off the bear and help Bodger regain his strength through a meal Tao provides. Together, they continue their determined trek towards home.
Challenges mount as the animals reach the perilous sawmill area, where Bodger tries to steal food, only to be shot at by the vigilant chef. Responding quickly, Luath manages to catch a rabbit to sustain them, but they later encounter Jeremy, an elderly hermit who mistakenly welcomes them as guests. After a brief, chaotic meal where Jeremy consumes it all himself, the trio continues their quest, facing a swift river crossing that results in Tao being swept downstream.
Miraculously, an angelic figure named Helvi rescues Tao and tends to his wounds, restoring his strength with the help of her parents. Meanwhile, a fierce thunderstorm looms, and just as Tao sets off to reunite, he must evade a hungry lynx, thwarted only by a hunter's timely intervention.
As they come back together, they face further trials, including a prickly porcupine that leaves Luath wounded. Fortunately, he's discovered by James Mackenzie, who takes him to his warm farm where Bodger has already found solace with Mackenzie’s wife, Nell. That evening, the dogs are cared for, while back at home, Longridge and Mrs. Oakes scramble to understand the unfolding events, prompting a desperate call for assistance as sightings of the animals begin pouring in.
Finally free, the trio must navigate the unforgiving Ironmouth Mountains, where the harsh winter conditions threaten them with isolation. The Hunters learn that James was the last to see their beloved animals alive. During this time of distress, Elizabeth struggles against the disheartening truth of their situation, while Peter and Mr. Hunter succumb to the sorrow of possibly losing Bodger and Luath. In a bid to uplift their spirits, they host a birthday celebration for Peter, attempting to sidestep the grim reality closing in.
As the night crescendos with excitement, Elizabeth hears a familiar sound echoing from the shadows outside — it could only be Luath. With hope, she urges her father to use his whistle and call back their loyal hound. When Luath emerges, joyously reunited with Tao, the siblings rejoice, yet Peter's heart is heavy, as Bodger has yet to return. His gaze sweeps over the darkened night until, like a beacon of hope, Bodger appears, his once-energetic stride tempered by age but unyielding in his loyalty. Together with Luath and Tao, they stand united once more, embarking on the next chapter of their incredible journey, a testament to the unbreakable bond of friendship.
