Captain Frank Harris is undergoing Interceptor simulation tests, but despite being the most experienced and oldest of the pilots, he only barely passes. Alec Freeman believes Straker is about to fire him, but the commander simply wants him to keep an eye on him. When Harris returns to Moonbase, a real UFO is spotted and the Interceptors are launched, but he is concerned that he will make a mistake and end his career…
A UFO arrives on Earth and collides with General Henderson’s car as he returns from a vacation in America, causing a crash and injuring him. General Calper, who accompanies Straker in a ShadAir jet, takes his place at an International Astrophysical Commission meeting. Calper is hostile to SHADO, but a UFO is spotted homing in on them in flight.
Dennis Skipton, a SHADO technician, has created an invisible force-field and shows it to Straker and Freeman by setting it up in the control room and walking into it! Six UFOs enter the solar system, change course, and disappear before Straker can take any further action! Six more UFOs are tracked while attempting to determine their location, and their path leads them to Mars.
Over the Arctic, Sky 1 piloted by Peter Carlin, is crippled by a UFO. He is forced to warn another craft, a US Army plane piloted by Lieutenant Braydon and Sergeant Lucas, to stay out of the area before colliding with the UFO and crashing it. The Army plane, which is observing the attack, has also encountered difficulties in the worsening blizzard and crashed nearby, as the Alien survivor has observed…
Sky 1 intercepts a UFO and shoots it down over the North Atlantic. The Alien survives and is caught in the net of a new high-tech fishing vessel, where he murders the crew. A signal is sent out, instructing the skipper to make a bomb, in order to lure Skydiver into a trap. The metal fishing net ensnares the skydiver, and the Alien throws an explosive on board. The Alien, however, has forgotten about the skipper, who harpoons the Alien, allowing Carlin to grab the bomb and throw it into the sea before it explodes.
A highly classified chemical known as 12X, which is used in rocket fuel, is being transported to a new international space base in Cornwall. A UFO eludes detection and is tracked as it approaches the area. After destroying the escort, the Aliens hijack the tanker and transport it to a decommissioned chemical plant.
As an alien ship approaches, astronauts Skipper and Alvin try to repair their ship, but a helmeted monster informs them that their time is up! Also, cut! Sol X. Zimenes congratulates his cast on a “great moment,” but Buzz Peters, who plays the alien “Terror of the Spaceways,” is not impressed and storms off.