In the Pacific Ocean, Skydiver is alerted to a UFO estimated to arrive in their area. Captain Carlin launches Sky One but as he approaches the UFO, his missile launching system fails and he has to use cannon fire. The UFO also fires, and Carlin is forced to ditch in the sea. With communications also out, Carlin is amazed to see an old warship nearby, and swims over in the hope of finding a working radio. As a SHADAir rescue plane is ordered to search for Carlin, the captain finds the warship deserted except for dummies – and the Alien of the crashed UFO in the radio room. Carlin is now a prisoner, and the Alien has undoubtedly called for help. Carlin tries to fight the Alien, but the spacesuit is like armour and the captain comes off worse. Forty miles away, the World Navy are launching their new ‘Barracuda’ tactical nuclear torpedo – at the target warship! As the SHADAir plane, carrying Paul Foster, enters the strike area, it is warned off. Foster takes his chances, and spots the unconscious Carlin on the deck of the warship. But as he tries to get a stunned Carlin clear, the Alien re-appears and shoots down their ladder. With time against them, Carlin and Foster dive over the side, back to Sky One, and take it underwater as the missile destroys the warship, Alien, and arriving UFOs.