Captains Scarlet and Blue catch a courier and a business man in the act of an illegal biological weapons sting operation, but upon the retrieval of the contents, they find that they have been duped. Destiny Angel and Lieutenant Green take a much-needed vacation at the lunar base. Scarlet tracks down the informant and confronts him, only to find out that the weapon is on the moon base. Upon arrival, Scarlet warns the leader of the moon base of the biological weapon, who immediately initiates the lunar tour to allow the Spectrum agents to search the base, but it is revealed that Captain Black is holding the tourists as hostages in their vehicles in his Bison moon vehicle, coaxing Captain Scarlet into a duel to prevent the destruction of the moon base.
—Christopher Smith