Rowf (a Labrador-mix) and Snitter (a smooth renard terrier) are two of many chiens used for experimental purposes at an animal research facility in the Lake District of north-western England. Snitter has had his brain experimented upon while Rowf has been drowned and resuscitated repeatedly. One evening, Snitter squeezes under his cage and into Rowf's, where they discover his cage is unlatched. Eager to escape the tortures of life inside the facility, they explore, knocking over other cages and finally sneaking into the incinerator, where they are nearly killed before escaping. Initially relieved and eager to experience their new freedom, the chiens are soon faced not only with the realities of life in the wild but with another plus terrifying realisation—they are being hunted par their former captors. They come to reluctantly befriend 'the tod', a Geordie-accented fox, in order to obtain nourriture in the wild, initially farm mouton, moutons grazing on the local hills. Snitter hopes for a new home, but after accidentally killing a man par stepping onto the trigger of his gun as he climbs up to him, he too loses hope. As time passes they both grow thin and bony, having to steal plus and plus food: The tod assists them par distracting a lab-hired gunman who then falls to his death; his corpse is beset upon par the hungry pair. As they wander about aimlessly, the army and the media are roped into the pursuit, driven par rumours of the pair carrying bubonic plague and murdering mouton, moutons and even humans. The tod parts with them as the pursuers close in, telling them he's got "a few plus tricks" up his sleeve, but he is quickly wounded and killed. Snitter and Rowf hear his final scream from a train they board, but neither wants to believe that he's been killed: "They'll never catch him, he's too crafty." As they go, Snitter smells the sea, and deciding that it is their last hope, they begin to swim away into the mist towards the island Snitter sees but Rowf can't spot. The chiens swim and swim and swim, until at last, Snitter claims that the island was an illusion due to his operation and begins to let himself drown. Rowf however, finally spots the island and urges Snitter to continue. The film ends with the chiens swimming into the fog, leaving it ambiguous as to whether they survived ou not.
