The Second Doctor, Jamie and Victoria are enjoying themselves on a beach in Australia when the Doctor is subject to an assassination attempt. The controller of the would-be assassins, an agent named Astrid Ferrier, rescues them by helicopter. She takes them to her boss Giles Kent. It seems the Doctor is the physical double of Salamander, a ruthless megalomaniac who is dominating the United Zones Organisation in the middle part of the twenty first century. Salamander has ascended to power via exploiting new technology to yield more food, concentrating and harnessing the sun’s rays to generate more crops, but is set on increasing his power. When Kent, who was once Deputy Security Leader for North Africa and Europe, crossed Salamander, the dictator ruined him and removed his various allies. The only remaining Kent ally with any authority is Alexander Denes in Central Europe. The Doctor is persuaded to impersonate Salamander as a way of gathering more information on his designs. His first test comes when Kent’s home is surrounded by security troops and their leader, Security Chief Donald Bruce, arrives.
Bruce is a bully who intimidates those in his path, but the Doctor’s impersonation is strong enough to persuade him that he is Salamander – even though the real Salamander is supposed to be at a conference in the Central European Zone. Bruce leaves, albeit with suspicion, while the Doctor turns on Kent, realising he called Bruce there himself to test the impersonation. The Doctor is not yet convinced Salamander is a villain, but Kent presses ahead with a plan. Jamie, Victoria, and Astrid are to infiltrate Salamander's retinue while he's still in the Central European zone, via Denes’ support, and gather evidence on Salamander. Meanwhile, Kent and the Doctor will travel to Salamander's research station in Kanowa to gather intelligence there.
The real Salamander, in the Central European Zone, warns that a dormant volcano range in Hungary is about to explode. Denes does not believe this is possible and resist the calls to send pre-emptive relief. Jamie, Victoria, and Astrid have by now reached the Central European Zone. Jamie is to try to infiltrate Leader Salamander's retinue, while Astrid contacts Denes for a meeting. Jamie manages to get himself promoted to Salamander’s personal staff by preventing a bogus attempt on the Leader’s life, and also ensures Victoria is given a position as assistant to Salamander's personal chef. When Astrid meets Denes she tells him of the two spies who have entered the Leader’s staff.
Salamander now works on Denes’ deputy, Fedorin, to turn him against Denes. Fedorin is a weak man and gives in to Salamander’s blackmail easily, but is scared when he hears the prediction that Denes will soon be killed and Salamander will be asked to take over the Zone following the imminent natural disaster. On cue an earthquake begins as the promised volcanic eruption starts. Donald Bruce arrives but is unable to mention the Salamander in Australia issue before Denes returns to the palace too, blaming Salamander for somehow engineering the volcano. Salamander responds by saying Denes failed to heed his warnings on the volcanoes and is thus negligent and must be removed from office.
Denes is arrested and Salamander now tells Fedorin to poison him before he can be brought to trial and repeat his allegations. When Fedorin fails to do so, Salamander uses the poison on him instead.