The Door Into Summer is one of Heinlein's more prophetic stories. The main character, Dan Davis, is a sort of edisonian inventor/engineer with a talent for thinking out neat gadgets that is probably only rivaled by Heinlein himself.

In the course of the story, Dan takes us through the engineering needed to invent a dictation (speech to text, that is) machine, computer aided drafting, the water bed and, of course, the household robot. In addition, we peripherally see the hospital delivery robot, the automatic teller machine and assorted minor gizmos. Few stories in the entire annals of science fiction contain so many glimpses of the future that actually came true.

The plot is, for a time travel story, unusually straightforward. Dan invents his way past his problems and, eventually, gets the girl of his dreams.