When Shifty (15) and Scabs (12) visit their cousins on the Scottish island of Farrensay, they are horrified at the change. Jack (12) had been fun, impetuous, daft and very kind. The new Jack is obsessed with cleanliness, neatness and order. Milly (10) had been mischievous and cheeky. The new Milly is proud to be perfect. Shifty and Scabs desperately want their old cousins back.

Shifty hatches a ridiculous plan. They embark upon on an adventure to uncover the truth aided by a pig with attitude and a bumbling family friend, who is more of a hindrance than a help, but has a much-needed boat. The quest is fraught with silly mishaps on a boat overcrowded with six humans and a large pig as they race against time to uncover an evil plot.