The Mysterons vow to assassinate the Triumvirate of Europe, which comprises Presidents Conrad Olafson, John Henderson and Joseph Meccini – the three most powerful statesmen on Earth after the World President. Breaking into the rural home of electronics professor Gabriel Carney, Captain Black uses a sniper rifle to gun down the expert, who is then reconstructed by the Mysterons to carry out the threat.
To protect the Triumvirate, Spectrum moves each member to a different secure facility. Carney's reconstruction drives to Vandon Maximum Security Base, which is holding President Olafson, and rigs a loudspeaker system to blare out sounds of machine guns and tanks to fool the guards into thinking that the base is under attack. As the Angel squadron bomb the surrounding woodland, Carney cuts through the base's wire fence and drops an explosive device into an air vent that he believes leads to Olafson's underground accommodation, not knowing that it is actually a dummy. The base above ground is destroyed in the resulting explosion but Olafson is unharmed.
Sometime after this, the body of the original Carney is discovered. When word reaches Cloudbase that a second Carney has recently been seen, Colonel White realises that the Professor has been taken over by the Mysterons and dispatches Captains Scarlet and Blue to Carney's home, where the officers find a mysterious note reading "123 OHM". Scarlet deduces that this is Carney's assassination timetable: he attacked President Olafson first, so President Henderson is second and President Meccini third.
Returning to their Spectrum Pursuit Vehicle, Scarlet and Blue chase Carney's car as the Professor speeds to the facility containing Henderson. Carney activates a device that blanks the SPV's viewing monitor, forcing Scarlet and Blue off the road. Proceeding to the facility to secure Henderson, Scarlet and Blue find themselves cut off from external contact when Carney flies a specially-adapted toy plane over the complex, jamming all radio transmissions in the area. After using a grenade to blow up the facility's electrical circuits and cause a blackout, Carney dons night-vision goggles to avoid the disorientated guards while making his way to Henderson's quarters armed with a gun. However, as he enters the room, he fails to spot a tripwire, stumbles over it and is shot dead by Scarlet. Scarlet and Blue note that for all of Carney's electronics expertise, his reconstruction was defeated by a simple security measure.
- David Lee's script reveals that the original Carney was the designer of the electronic security systems at Spectrum's maximum security bases, which explains how his reconstruction is able to outwit the organisation.
- A scene that was scripted but not filmed shows the Carney reconstruction disposing of the original's body with the aid of a remote-controlled lawn mower.