With their death-defying exploration of Mars and groundbreaking discovery of primitive Martian life, Viktor and Julia have become history's most famous astronauts.

Now, after a series of exploits deemed reckless by space agency bureaucrats, they are being pressured to retire and spend their remaining days handling agency publicity. Fortunately, the Mars mission's primary financier, billionaire John Axelrod, has the political muscle to reassign them to an ongoing Pluto mission before it's too late; but the trip has a price tag: rescuing Axelrod's zealous astronaut daughter, Shanna, from a calamitous exploration of Pluto's frozen methane surface.

By the time Viktor and Julia reach the outer solar system, however, Shanna has not only set foot on the planet surface but also established contact with a walruslike native creature known as the zand. Together, the three astronauts must forge a tenuous union to unravel the mystery of Plutonian life.