The Door Into Summer

1970. A.D. Daniel Boone Davis is an inventor of household robots, who's been cheated out of his patents and company by a conniving friend and girlfriend, who stop just short of killing him, but instead send him into the future via suspended animation (a.k.a. 'Cold Sleep'). 2000 A.D. (Heinlein was a technological optimist!) Dan wakes up and finds that the descendants of his robots are among the most successful household appliances of all time. After he's identified as the original inventor, he makes a living as a promo figurehead for the company producing the robots. One day he chances across someone who's built an experimental time-machine and cons the guy into sending him back to a particularly critical moment before everything went wrong in 1970. 1970 A.D. Dan fixes what needs to be fixed to make things right in the future, then goes back into Cold Sleep, this time with his cat, 'Pete', whom he originally had thought lost; but now we know why that had to be soâand why everything just had to be as it was initially. 2000 A.D. Dan is united with the woman he's going to marry (who also did some 'cold sleeping' to get to 2000). Why it's top of the list: Because it's the most consistent, well-though-out, contradiction-free and elegant time-travel story ever. Time-travel 101. Would make such a great movie! Some future-world projections are antiquated, but that applies more to robotic technology, AI, and suchlike. There's also some utopianism about 2000 A.D. that definitely didn't pan out. For one thing, Heinlein thought that the world would get better. It didn't. But apart from that the plot is logical, and everything ends up making perfect sense, with not a paradox in sight.