Kevin McCloud follows architect Peter and his TV producer wife Emily as they take on the challenge of building twin conjoined houses in London - the plan being to sell one of them to fund the one they will eventually live in. They already have business partners - and potential new neighbours - who have bought into the scheme. Now all they need to do is build the houses. But from the start they are dogged by financial issues - not to mention problems with the experimental nature of the design. Can the two couples retain their friendship?