Her human friend, Isla, is sad, and if Isla's sad, then Heather's sad. 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.

Heather Duroc is an extraordinary pig, and she's happily hiding in London Zoo. But Isla is missing Scotland . . . When Heather traveled hundreds of miles to find her best friend, a girl called Isla, she never thought that she might end up undercover and on the run. But life at the zoo is sweet - there are plenty of apples and other pigs, and Isla visits every week. But Isla is sad and Heather knows she must help her friend win back the farm. She'll have to break out of the zoo, avoid being captured by horrible Mr Hornbuckle and, of course, work out which direction leads back to Scotland and the farm. The biggest challenges require the strongest hearts, so Heather must ask herself, how big is hers?