Maurice Gray, still based at Woomera Rocket base in Australia, is now a qualified radar technician. He elects to become a permanent member of the Mars colony, knowing that he is unlikely to be able to return to Earth. His uncle, Leslie Yorke, is unable to join him because of a heart condition, but approves his decision.
Gray joins other scientists on the spaceship ‘E5’, led by Professor Häller, and travels to Mars. They nearly suffocate when the ship's hull is holed by a meteorite, but are able to repair the air leaks in time. They receive a fragmentary message in Morse code from Mars, warning them of danger, and advising that they should return to Earth. Unable to easily do so, because of fuel and navigational difficulties, they continue their journey and land on Mars, near the plastic domes of Lowell Base.
All the colonists, including Mellor and Talbot, are safe, but an explosion has damaged the air-conditioning plant, and several domes are in ruins. Their air supply is now limited, unless emergency repairs can be made.
Miroff, a new-arrived astronomer, panics. He and two colleagues take off in one of only two usable rocket ships, bound for Earth.
More damage is done to the air-conditioning, and all the staff work feverishly to repair it and re-inflate the plastic domes which are still usable. Gray and Talbot travel by ‘dust-car’ to the other base, Pickering Dome, which has been out of radio contact. They discover that Professor Whitton and his colleagues have managed to breed plants, native to certain areas of Mars, into giant varieties that can produce enough oxygen to keep the domes inflated and liveable indefinitely. But the plants die once used, and the colonists are unable to generate enough oxygen to take them to Lowell.
In a desperate act, Gray and Talbot launch a cannibalised rocket E2, with just enough fuel to get them within radio range of Lowell. The latter is evacuated, and all colonists travel to Pickering, which is now crowded, but safe.
The story makes no mention of the carnivorous gastropods and pterodactyl-like flying creatures encountered in the previous story.
