Rama II: Arthur C. Clarke and Gentry Lee

Rendezvous With Rama told of the 2130 arrival of a mysterious, apparently untenanted spaceship, which during its visit, uncovered may wonders but answered few questions. One thing was clear - everything the enigmatic builders of Rama did, they did in threes. Now, in 2200, four years after a second approaching spacecraft has been detected, Earth knows what to expect and is ready to mount an expedition which may answer some of the questions posed by Rama.