An ambitious couple set out to build a revolutionary eco home in the Cotswolds, which will not only use very little energy, it will also produce four times the energy it needs. Environmental consultant Duncan is planning to manage the project himself, moving out of the London home he shares with solicitor Liz to live near the site. But although he is totally committed, he has never faced anything like this before, and almost inevitably the technically complex 18-month build, while living apart takes its toll on the couple.