On her second voyage to Mars in 2026, the crew of the nuclear powered Asclepius II enjoy a nearly flawless two month journey to the 4th planet ... until their flight computer mistakes a minor isolation box incident for catastrophic cabin decompression, and initiates the real thing, pitching the Captain of the ship into the vacuum of space, and blowing the expedition's chief exobiologist, Joan Desaliers, overboard in the escape pod, which thinks it's landing on Earth. Desperate to recover her before it lands, second-in-command Ted Schmit causes the death of two more of his crew, and dooms Desaliers, of late also his lover, to be the first person to walk on Mars, and the first one never to return to Earth.