From about 1969 to about 1973 Niven wrote five deliberately goofy stories about a time traveler from the middle of the thirty-first century. His job is to retrieve extinct animals from the past – and in the year 3050 pretty much all animals are extinct excepting people and dogs – and bring them to a private United Nations zoo. Hilarity ensues. Well, ‘Hilarity’ might be overstating it, but they are cute funny little stories that aren’t perhaps as tight as one would normally expect from Niven, but that’s part of their charm.
These retrieval missions never go quite the way Svetz expects. For instance, in one story he’s sent back to the middle ages to retrieve a horse. Having only one badly-deteriorated picture of a horse from a thousand-year-old children’s book to go on, he botches it and brings back a Unicorn. (And he’s mistaken for a wizard in the process) In another, he’s sent back to catch a Gilla Monster and brings back a fire-breathing dragon instead. In yet another his time machine jumps the tracks and he ends up in a world where wolves evolved to fill the human niche, while our simian ancestors never evolved and are simply ‘meat animals’ for Canis Lupis Sapiens. (Or perhaps "Lycanthropis Sapiens?" Try to come up with your own taonomy for this kind of thing, it's fun!) In another he screws up the timeline so badly that the future ceases to exist until he fixes it. In yet another he meets up with Death Incarnate, who turns out to be a time traveler from yet another alternate timeline that was similarly wiped out by screwing around with the past.
As I say: Deliberately goofy stuff, but fun.
In 1999 Niven decided to revisit Svetz and the rest of these characters in a book called “Rainbow Mars” in which they discover that Mars actually *was* inhabited up until late medieval times, and so a combined Space Force/Time Agency mission to check it out. It seems Mars in 1000 AD has a massive, massive tree growing out of it, reaching from the ground all the way to orbit, and the UN feels that getting some seeds for this and growing a similar tree on Earth would provide easy access to space. (In the 31st century, access to space is just as annoying, expensive, and dangerous as it is in the 21st century) Alas, they haven’t thought through the potential repercussions of importing a piece of (hyper)megaflora of this size, which provides most of the fun of the second half of the book.
A fairly short novel at 222 pages, which makes it only about 85% longer than your standard Hardy Boys mystery, but it recaptures the giddy fun of the old Svetz stories in a way that I frankly didn’t believe Mr. Niven still had in him. Mars is a deliberate pastiche of a half dozen or more competing SF tropes. We meet up with four-armed green martians and space blimps from Edgar Rice Burrough’s “John Carter” stories; some abandoned Martian homes straight out of Bradbury’s “The Martian Chronicles”; the tall, spidery Martian cities of Heinlein are now ruins; a couple of the endlessly fascinating (And slightly disturbing) Martian Aliens from Stanley Weisbaum’s largely-forgotten-but-brilliant pulp stories from the 30s show up, as do several of C.S. Lewis’ competing martian races (!). And of course what kind of a party would it be without H.G. Wells’ octopoidal aliens showing up and telling us to get the hell out when things get a little too wild and we start breaking stuff? The reason for this bizarre mélange is directly tied in to the ongoing plot device about how Svetz goes in to a fantasy world every time he travels in to the past, and – to my surprise – it makes sense. (Something the original stories themselves never quite did).
The book is padded out with the final 94 pages making up a sort of acromegalous appendix that includes all the original short stories involving these characters, despite the fact that all these stories take place *before* the novel itself. This is probably a mistake, since I imagine most people (like me) haven’t read these stories in 20 or 30 years (They're not particularly famous, as a series), and are probably somewhat lost as to what is going on without them. So if you *do* read the book, start at page 223, read to the end, and then go back to page 1 and read forward from there.