Transmitting to Earth, the Mysterons (voiced by Donald Gray) vow to destroy the undersea World Navy base Atlantica. In view of this threat, Spectrum take over an operation to bomb and disperse a wreck that is drifting towards the base. Captains Blue and Ochre (voiced by Ed Bishop and Jeremy Wilkin) are selected to carry out the mission and briefed at Maxwell Field, where they conduct themselves with uncharacteristic flippancy and absent-mindedness. Before taking off in their V17 bomber, they encounter a man whom they fail to recognise as Captain Black, who switches their flight plan.