Corporal Benton overhears about the bomb and informs the Brigadier. The Brigadier instructs Branwell to keep out an eye for the bomb while heading back to London.
Vaughn, enraged by the Cybermen's betrayal, uses the Cerebrator to destroy the Cyber-Director. The Doctor suggests disabling the radio signal since the bomb will follow its path. Vaughn calls for Packer, but the Cybermen have taken over. A Cyberman kills Packer and the Doctor destroys it with the Cerebrator. He then calls the Brigadier for help. Vaughn agrees to help because of his hatred for the Cybermen and the Brigadier sends a helicopter.
Captain Turner has contacted the Russians and they've fit the rocket with a warhead to attack the Cybermen. UNIT organizes what it can to attack the Cybermen while the missile base keeps a lookout for the Cyberbomb.
The Russians launch their rocket. The Doctor takes the UNIT helicopter into the heart of the IE complex. He and Vaughn sneak past the Cybermen as UNIT rolls in and attacks. A furious battle rages and UNIT prevails.
Vaughn is about to enter the radio tower when the Cybermen attack. He fights them with the Cerebrator but is killed. The Brigadier arrives just in time to save the Doctor. They then destroy the radio transmitter.
Sergeant Peters spots the Cybership coming in to deliver the bomb. The Russians redirect their rocket to intercept but the Cyberbomb is launched before it can hit. Branwell uses his remaining missiles to take it out. The Russian missile then destroys the Cybership, ending the invasion.
Captain Turner and Isobel, now famous for her photos of the Cybermen, escort the Doctor and his companions back to the TARDIS. They put the repaired circuits in and take off.