Drifter the Border terrier is having a miserable day - it is raining hard on the hill in Somerset where he is meant to be rounding up sheep, and an unwanted visitor in the shape of a lurcher has already got him into trouble over some stolen biscuits. Even so, he is prepared to pretend to be a sheepdog to keep his owner Rosie the Vet - known and loved by Drifter as The Two-Legged Giant - happy. However, when the timid sheep Maisie manages to frighten herself by looking into a pool of water and runs away, Drifter has to step up to the mark - can he become a real sheepdog, find Maisie, bring her back to the shed and save the day? And will it ever stop raining? And will The Two-Legged Giant discover who was really responsible for stealing her biscuits?