The day before UNIT is to hand over operations to Britain’s Internal Counter-Intelligence Service, both UNIT and ICIS are called out to do battle with a group of Silurians at Tower Bridge. BBC reporter Francis Currie tries to get footage of the attack, but ICIS’ Sergeant French knocks him out, confiscates his camera and has him locked him up back at UNIT HQ. Once the fighting is over, French reports to Captain Andrea Winnington of ICIS and tells her to inform Colonel Brimmicombe-Wood of UNIT that their troops took no prisoners. UNIT’s press officer, Colonel Emily Chaudhry, tells the press that the explosions on the bridge were caused by subsidence, and that UNIT and ICIS were assisting emergency services.
The next day, Winnington escorts the retired Sir Alistair Gordon Lethbridge-Stewart to the press conference; since he was present when UNIT was founded, it’s been decided that he should be present at its end. Their car is forced off the road by a helicopter, and their driver is shot dead; however, Sir Alistair manages to shoot down the helicopter, which crashes in flames. When Sir Alistair and Winnington examine the wreckage, they find that their attackers were a human and a Silurian. Winnington tells Sir Alistair that her troops “put down” a party of Silurians last night, and although Sir Alistair raises an eyebrow at the terminology, he assumes that he’s been targeted due to his actions against the Silurians 30 years ago. An escort picks up Sir Alistair and Winnington and delivers them to the press conference, where Colonel Chaudhry takes Sir Alistair to a quiet dressing room where he can rehearse his speech.
Francis Currie has been held in the cells overnight while Sergeant French tries to convince him to sign a waiver promising not to report what he witnessed. When Currie refuses to do so, French accuses him of becoming belligerent and “defends himself,” leaving Currie just about capable of signing the form. As ICIS troops take Currie to the sickbay to recover from his “nasty fall,” Winnington tells French of the earlier attack. She and French assume that it was she who was targeted and not Sir Alistair, but then another Silurian breaks into the building and is spotted heading straight for Sir Alistair’s rooms. Chaudhry hears but ignores the alarms, as it is now ICIS’ job to deal with such problems -- but as she sets up drinks for the journalists, a soldier informs her that someone wants to speak with her...
Sir Alistair is rehearsing his speech when a Silurian breaks down his door and confronts him, addressing him as Brigadier and using its third eye to force him to drop his gun. By the time Winnington and French arrive, however, Sir Alistair is alone and is calmly finishing his drink. He tells them that the Silurian tried to convince him it was seeking peace, but he saw through that claim and left it dead in the restroom. He’s called in Chaudhry to help clear up the mess, and Winnington and French leave them to it, convinced that this security breach just confirms that it’s time for ICIS to take over the reins from UNIT. However, Sir Alistair informs Emily that he has a surprise in store for ICIS, and the incident with the Silurian has removed all doubt that he’s doing the right thing.
The press conference begins, and Emily introduces Sir Alistair to the press. Due to the nature of his covert work, the public is generally unaware of who he is and what UNIT does; however, they have some vague idea that significant changes are occurring in national security, which is why this press conference has been called. But rather than delivering a vague and non-controversial speech about the handover, Sir Alistair tells the startled journalists that, for the past several decades, UNIT has protected the world from unnatural and extra-terrestrial threats, and now, they’ve made contact with a species that seeks peaceful co-existence with them. Sir Alistair thus introduces the press to Orgath, the Silurian ambassador who contacted him in his dressing rooms.
Winnington draws a gun and tries to shoot Orgath, insisting that the Silurians just want to wipe out humanity and take the Earth for themselves -- but although Orgath defends himself by using his third eye to force the gun out of her hand, he goes no further. Instead, he informs the assembled journalists that the battle at Tower Bridge was provoked by ICIS troops, who slaughtered a diplomatic party trying to make peaceful contact under a flag of truce. Winnington tries ordering French to place Sir Alistair under arrest for treason, but finds that French has himself been arrested for assaulting Francis Currie, who went straight to Emily Chaudhry when he was released from UNIT’s sickbay. Winnington has just tried to kill an ambassador live on BBC1 news, and now UNIT will have to remain in control of alien matters on British soil so that humanity can present a united front during this all-important first contact.
Winnington is placed under arrest, but remains convinced that her actions were justified and that Sir Alistair has betrayed his country and left it open to attack from outside. However, the journalists are more willing to listen to Orgath, who assures them that most of his people acknowledge the sophistication of human culture and seek peaceful co-existence. As Orgath addresses the crowd, Sir Alistair and Emily agree that it would be best if he were to slip away quietly now, leaving Emily to deal with the fallout of events. Colonel Brimmicombe-Wood is on his way to UNIT HQ with the Prime Minister, and while they wait, Chaudhry opens up the floor to questions and takes the first one from Francis Currie.