Alex Rose thought he was through with space exploration. He had explored the unknown depths of Jupiter's Great Red Spot and made the greatest discovery of his time, a reef of life full of strange inhabitants. Now he and his wife, the lovely Sensor clone Mary Seventeen, lived a quiet and happy life on Ganymede. But their contentment was shattered by a summons to participate in an even greater challenge: the first faster-than-light mission to another star.

Fleeing an Earth divided by war, the first starship Goddard, a gigantic self-contained biosystem with a crew of over a thousand, was to travel to the red dwarf Lalande on its maiden voyage. Alex and Mary, with their shuttle Diver, would call on their experiences in Jupiter's reef to explore an ancient gas giant orbiting the star. Since a reef of complex and possibly intelligent life had naturally evolved on Jupiter, what alien life - or even civilizations - might have developed on a much older planet? The answer they find proves to be a stranger and more perilous adventure than even Alex and Mary could have imagined.