Once again, the Mysterons target the Spectrum Angels in their latest act of retaliation, but it isn't actually one of the Angels, it's one of their home cities.

Receiving a report from a biological research station on the outskirts of Manchester, England, regarding the theft of the phial of the K-14 virus. This is a revolutionary, & brand new strain, that has the capability to kill 10 million people. Captain Scarlet and Captain Blue start a timed race to find the station's research assistant suspsected of the theft, who is the only person to be granted access to it, Judy Chapman.

Assessing that the forces' target is the Boulder Dam of Los Angeles, which the city's name stands for ""The Angels"", Scarlet places his non-indestructible life, in this particular case, on the line, to recover the phial, although he to faces imminent death.