The real story begins when Waldemar the Tenth dies. His successor, Waldemar the Eleventh, has his eye on the stars rather than the past. However, faster-than-light travel is still only found in fiction. The powers-that-be have a brilliant idea -- go back in time a thousand years or so and launch a ship toward the nearest star. Once you get there, establish a colony, leap back in time and send a message back to Earth. The trouble with that idea is that no one told these visionaries that the time machine itself weighs almost four million tons.

A more realistic goal is set -- Mars. Everything indicates that there was life on Mars in the not-so-distant past. Time-travelling probes sent to Mars reveal vegetation, alien civilizations, and most startling, an incredible monolithic tree that reaches into space. Convinced that this is the key to the stars, a living space elevator, Svetz and two female companions are sent to Mars to collect seeds, bring back aliens, and determine what happened to life on Mars.

What should be a straightforward mission becomes complicated. They discover at least five different species that appear to be at war with one another as their civilization crumbles. The various aliens pursue the strange visitors in an effort to gain an advantage over their rivals. Worse, the tree, dubbed the skyhook tree, has become unrooted from the soil of Mars and they can't seem to locate any of its seeds.

Rainbow Mars takes a light-hearted look at time travel, environmentalism, and the possibility of life on Mars. The book jacket says: "thought provoking, vivid, viciously smart and wildly funny." Thought provoking and vivid -- yes. Viciously smart and wildly funny -- well, no. Humorous and intelligent, definitely. Niven take the concept of an orbital tower, an elevator to the stars, and plays with the idea of it being organic rather than mechanical. Kind of turning the whole Ringworld concept on its ear. What if instead of constructing a huge technological wonder, you grow it? Then throw in time travel and all of the complications that accompany it. Thankfully the story is not filled with painful, mind-wrenching time-paradoxes that can make time travel tedious and confusing.

There's an excellent piece at the end by Niven explaining where the initial idea came from, and how the story evolved. I think you'll enjoy Rainbow Mars. It's clever, humorous and an enjoyable book. Just remember to start at the end before you go to the beginning.