A deadly night attack on an army base. Vehicles are destroyed, building burned, soldiers killed. The attackers vanish as swiftly as they came, taking highly advanced equipment with them.

Metal figures attack a shopping mall. But why do they only want a new games console from an ordinary electronics shop? An obscure Government Ministry is blown up — but, in the wreckage, no trace is found of the secret, state-of-the-art decoding equipment.

When the TARDIS returns the Doctor and Martha to Earth from a distant galaxy, they try to piece together the mystery. But someone — or something — is waiting for them. An old enemy stalks the night, men no longer made of flesh...