Pathfinders to Mars is third in a series of shows that started with Target Luna and Pathfinders in Space.
The series opens with a secondary mission in a new rocket, MR4 (Moon Rocket 4), which takes off from Buchan Island for the moon. This time Henderson takes the lead role as pilot accompanied by Professor Wedgewood’s oldest son Geoff as radio operator, Professor Mary Meadows, Henderson’s niece Margret (Hester Cameron) along with Hamlet. However one of the crew turns out to be science writer named Harcourt Brown (George Coulouris) who has plans to divert the ship to Mars determined there is life on the planet. Brown succeeds in getting MR4 to Mars, but with the length of the journey, the crew decide that the only way to get home is to find water on Mars.
Thankfully, MR4 has landed within a hundred miles of the polar ice cap so the group set off, Brown too, believing there to be life on Mars. Encountering Lichens, crevasses and other perils, Brown is devastated when he discovers no intelligent life and feels cheated by the others. In doing so, he intends to leave the others behind on the planet. However, lichens manage to infiltrate MR4, stopping Brown and giving the Rocket crew a chance to overpower him.
However, Earth has moved out of the Martian orbit, thus, making the journey home impossible. Yet Brown creates a theory that if they can use the gravity pull of the Sun to get home. Some time after setting off, the crew all slowly succumb to gamma rays from the Sun one-by-one. By a miracle, there is a total eclipse and Mercury shuts of the rays from the Sun but they quickly find themselves being pulled into Mercury’s gravity pull.
The crew then realize that Buchan Island has made various satellite fixes on Mercury, thus enabling MR4 to make the home journey to Earth. As MR4 falls out of danger from the Sun’s gamma rays, Brown ponders of the idea of other life on another planet and sees Venus as a possibility…