The TARDIS brings the Doctor and Turlough to a high-tech scientific installation on the planet Testament in the distant future. The human race have become intergalactic buccaneers, thanks to their ability to generate vast amounts of power for long-distance travel. Testament is the source of that power – and the Doctor has never quite understood how it works. But experiments are underway on Testament - experiments with potentially explosive and devastating consequences. And even the Doctor may be too late to stop it. With politicians and bureaucrats getting in the way, the race is on. Not to stop a disaster - but to save as many people as possible.