Recorded between 17 and 19 March 1995, the team try to discover what a 2000-year-old underground chamber (fogou) beneath Jo May's garden was used for. Dowser Hamish Miller shows the extent of the fogou beneath the lawn, and Tony tries his hand at dowsing. But Mick is skeptical, preferring to rely on the geophysical survey. They are also trying to find the Iron Age settlement that would have adjoined the fogou. Joining the team are archaeological geophysicist Susan Ovenden, and county archaeologist Nick Johnson. The programme includes an experiment in extracting pure tin from the local stream.