Barnaby (Baz) and Cassandra (Cas) Geopardy are fourteen-year-old twins, hence the nickname Double Jeopardy. Their father is an antique dealer, and they are staying in a thatched cottage on a farm in 'The Cotswolds' (in the UK), while their father hunts for bargains in the district.
One day, at a local market in the town square, they see a man stealing apples and helping himself to other bits and pieces from the various stalls. The locals seem to let him steal from them. The twins are puzzled and they follow the 'apple nicker' to find out what he is up to, and in doing so they meet many of the locals, including a farmer's wife, who is not at all jolly (as farmer's wives are supposed to be). Then there's a secretive butcher, a librarian, a boy in a bike shop and an old woman who hoards newspapers. By piecing together a complicated story and various clues, they solve the mystery.
