Robert Maitland, a 35 year-old architect, is driving home from his London offices when a blow-out sends his speeding Jaguar hurtling out of control. Smashing through a temporary barrier he finds himself, dazed and disorientated, on a traffic island below three converging motorways. But when he tries to climb the embankment or flag-down a passing car for help it proves impossible - and he finds himself imprisoned on the concrete island.