The Door into Summer is a cutesy, if somewhat alarming time-travel story. Daniel Boone Davis is a brilliant engineer who has his home automation company stolen out from under him by his greedier partner and even worse ex-fiance. In a fit of pique, he decides to have himself cryonically preserved and thawed out in the year 2000. While he tries to clear up loose ends in the future, he finds that several vital technologies were just as he was planning on inventing back in the 1970s, and that the designer was a mysterious 'D.B. Davis.' There's a rat loose, which turns out to be a classified-but-working method of time travel invented by a disgraced physicist. Davis goes back to 1970, sets everything right, and then returns to the future to live a perfect life.

What works is the paradox-less timetravel, although not to the sheer density of "All you zombies." Time travel to the future is a old story, and future shock of this sort was made standard by H.G. Wells in "The Sleeper Awakens", but on the plus side this story came out a good five years before Ettinger's The Prospect of Immortality gave cryonics its first mainstream success. Some of the gadgets Heinlein predicted exist in some form; robotic vacuums and 3D drafting tools. Even wrong predictions about the future can be amusing. And while I am not a cat person at all, this is the best book about a cat that I know.

Where this goes wrong is hints of the weird 'late-phase Heinlein.' Much of Davis's character is driven by his love of his 11 year old "niece" Ricky (not a biological relationship), and the idea that her life might have gone terribly wrong when he had himself frozen. Well, there's lot to love about brave little girls, but proposing marriage to them and playing it as a positive emotional climax is just wrong even with various forms of time-travel. It's really moving, but the context of marrying an 11-year old who calls you "Uncle" is just too weird, and knocks this story down to three stars.