Ring around the moon

Maintenance engineer Ted Clifford is struck by an energy beam which transforms his brain into a computer relay station for an alien probe which captures the Moon within an energy ring. When Clifford's mind burns out, the probe seeks a new relay and a medical mission on the lunar surface provides it with the opportunity to capture Dr. Helena Russell. She later returns to Alpha, apparantly unharmed, but is revealed to be relaying information from the Alpha computer through an energy implant in her brain. In an attempt to free Helena from the probe's control before she suffers the same fate as Clifford, Koenig and Carter board the probe and discover that the computerised device is on a pre-programmed mission to destroy the human race!