Onboard a ship, the wheelchair-bound John Lumic unveils his latest creation, much to the horror of a scientist who insists he has to inform the authorities. Unhappy with this resistance, Lumic orders the mysterious metallic figure to kill him. It does so by electrocuting the scientist with its silver hand. Lumic decides to head for Great Britain...

After the Tardis suffers a technical failure, The Doctor, Rose and Mickey arrive in seemingly familiar London surroundings. But a look up above reveals several zeppelins cruising in the sky and Rose notices her apparently deceased father Pete's image on an advertising billboard. The trio soon realise they are in a parallel universe and cannot escape until the Tardis is repaired.

Mickey visits his alternative grandmother to try and ease his conscience, but soon finds himself kidnapped by a gang after being mistaken for a rebel leader named Ricky. The resistance group are fighting against Lumic's Cybus Industries, which they believe are taking homeless people off the streets for their own malevolent purposes. However, the gang soon discover that Mickey isn't Ricky when the real rebel returns to their headquarters.

The Doctor and Rose also discover the control Cybus has over society, as they see London's inhabitants grind to a halt when a signal is sent to the earpieces they all wear. They also uncover plans to hold a reception for Cybus Industries that evening at the lavish house of Pete Tyler, who is a succesful entrepreneur in this universe. The time travelling duo decide to sneak into the party dressed as waiters.

Meanwhile, Lumic is busy furthering his new project with the help of henchman Mr Crane. For the innocent victims are sent to a warehouse filled with hi-tech surgical machinery... and plenty of screams.

Britain's President is present at the Cybus party and the crowd eagerly await news from Lumic. Rose is slightly distraught by the less-than-pleasant nature of her parallel mother Jackie, who has a dog called Rose instead of a daughter.

Soon, a loud marching noise can be heard in the streets around the Tyler residence, as lorries pull up to release a small army of metallic figures. As they advance towards the house, The Doctor manages to see them in focus - and is shocked to discover that they are his long-term enemies the Cybermen. His foes violently break in and begin their quest to upgrade the world...