It's tough to summarize this book without giving away too much; I think that even the two-sentence Amazon.com summary reveals too much information. A modern reader, familiar with many of the sci-fi conventions which would have been new when this book was written, will quickly unravel what Heinlein probably fancied to be an elaborate plot twist if given more than just the basic details. I doubt that you will be surprised by any of the turns the plot takes, so I suggest that you keep yourself in suspense as much as possible so that when the twist occurs, it will be a bit more unexpected and therefore more enjoyable.
Here is my plot synopsis, scant on information though it is:
Dan Davis, an engineer who invents housekeeping robots, is suckered by his business partners and loses control of the company he founded. They force him to enter suspended animation for 30 years, and when he wakes up, he wants his revenge.
Yep, that's all I'm going to tell you. If you want more, you'll have to read it.
As I noted above, this is an old (or, if you prefer, "classic") sci-fi adventure novel. It features a rugged male protagonist, outmoded views on gender roles, plenty of smoking, boundless optimism about the imminent triumph of technology over pretty much everything, and an idealization of the "engineer" as a super-genius proficient in any and all things related to the field of "engineering" that could only have come out of the 1950s.
None of those characteristics are really disadvantages, however, because this novel doesn't try to offer astounding philosophical insights or remarkably prescient versions of the future. Instead, it is simply a rollicking good adventure combined with a love story involving a 12-year-old. It has a straightforward revenge plot that is nicely turned on its side when Heinlein provides the protagonist with a powerful new tool with which to exact his vengeance. Again, I don't claim that you will be shocked or amazed by any of the turns the plot takes, but the way Heinlein stitches the whole novel together is a delight.