At the Culver Atomic Centre, located in Yorkshire, England, Captain Black accidentally exposes himself to a short-term radioactive isotope, when detected by the security guards, causing his hesitation. Although the isotope is physically harmless, it makes him a straight-forward target when using radiation-tracking systems during Spectrum's full-scale manhunt, to uncover and apprehend the Mysteron agent.

But when the organisation is decoyed, Black manages to kidnap Symphony Angel, who disobeys direct orders from Colonel White. Instead of maintaining her aerial surveillance mission, she finds herself on death-row, in a radiation chamber, and Black in absolute control, with the judgment of killing her, or letting her go free.