After the Mysterons take over a Phoenix policeman named Rimmer and use him to steal a canister of deadly alien spores brought back by a space probe from Ganymede, Captain Scarlet and Captain Blue are ordered to give chase - but they are thrown off their trail when the Mysterons take over a biker named Brock and use him to carry out the plot instead. Meanwhile, Captain Ochre's Raid Bike is stolen by another biker named Colt.