While looking for her brother Jimmy (Richard Dean), Valerie (Gillian Ferguson) finds a calcified alien. Her scream sends everyone running. The alien is humanoid in appearance. Dr. O’Connell (Harold Goldblatt) determines that he is 400 million years old. It seems that the alien died around the same time that plants began on the Earth surface.
Professor Mary Meadows (Pamela Barney) and Dr. O’Connell begin documenting the alien symbols found around the cavern and on the spaceship. They send Valerie and Jimmy to help by having them write down the symbols they find further in the cave. In the farther reaches of the cave they find a child’s stuffed toy and a model spaceship. They also find what looks like a children’s book. The team now has evidence that there were alien children the alien ship’s passengers.
Eventually they find a way to open the spaceship. While the team is busy learning everything they can about the aliens and their way of life a meteor shower threatens both MR-1 and MR-2. The showers are being monitored by Jean Cary (Irene Sutcliffe) and he team at the Buchan Island Rocket Research Station but she is unable to contact Wedgwood and his team to warn them.
The control facility in the series is located in the fictional Buchan Island Rocket Research Center off the coast of Scotland. There was an actual Royal Air Force Base Buchan in Aberdeenshire, Scotland. It opened in 1952 as a radar center and was part of the ROTOR radar network. It had several upgrades throughout the years and was in use until 2004. It was then downgraded to a Remote Radar Head. There was also a real rocket base, the Isle of Wright, off the coast of England.