Two dogs, Snitter and Rowf, escape from a research laboratory in the Lake District where it is wrongly supposed they have been purposely infected with a deadly virus and now pose a dangerous threat to the human population. As the authorities give chase, the two friends make their way through the hills and across the moors, along the way learning to survive on their wits and finding friendship and help from a fox they encounter. They dream of finding their original owners and a safe haven - but the hunt is on.