A secondary mission in a new rocket, MR4 (Moon Rocket 4), to the Moon takes off from Buchan Island. 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 along with Hamlet. One of the crew turns out to be the science writer named Harcourt Brown. Brown has plans to divert the ship to Mars as he is determined to prove that 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.
