 When the Doctor, Zoe and Jamie investigate the mysterious disappearance of an eminent scientist, their search takes them to International Electromatics, a powerful firm run by the sinister Tobias Vaughan. Under surveillance by the Brigadier s top secret United Nations Intelligence Task Force (UNIT), it soon becomes apparent that there is more to Vaughan s activities than meets the eye. Just who are his mysterious allies? What is lurking down the sewers of London? Soon the Doctor discovers his ultimate horror - that the Cybermen are in league with Vaughan. As they begin bursting from the sewers onto the streets of London and cities around the world it is clear that their plan is the total invasion of planet Earth