Heather the pig is happily hiding in London Zoo. But something's wrong. Her human friend, Isla, is sad, and if Isla's sad, then Heather's sad. Isla wants to move back to Scotland. Can Heather help? No problem. She'll just break out of the zoo, work out where Scotland is, walk the 500 miles to get there, avoid being re-captured, confront a wildcat, defeat Mr Busby, and then get the farm back for Isla and her dad. Easy!