Duncan is the third clone of the founder of the Titan colony. The first generation, Malcolm, discovered a genetic defect that made it impossible for him to produce heirs. Thus every generation a new clone is created to carry on the family line and keep control of Titan. Duncan is being sent back to earth for the 500th anniversary of the American independence and of course to create his own clone replacement. He hopes to reconnect with a woman, Calindy, he met on Titan many years ago and to solve the mystery of what happened to his friend Karl when Calindy left. 

Not my favorite book by a long shot. While Clarke does a pretty good job of predicting some future technology, you can definitely tell this was written in the 1970s before the advent of the internet and modern technological breakthroughs. I found it interesting that supposedly in the future individual governments had become a thing of the past but they were still celebrating the 500th anniversary of America. There were a lot of nostalgic bits that I could have done without. Why the Titanic? And then the ending was all about contacting aliens. It just didn't work for me and I will admit that I skimmed a large portion of this because I was bored.