This is middle-period Heinlein, which means it is very readable in contrast to some of his later stuff that is for hard-core fans only. The viewpoint character is an engineer, Daniel Boone Davis, who is developing robotics. He has some good inventions, but some very bad business partners who cheat him. Cryogenics and "cold sleep" allow people to travel into the future, so he does that, only to find that there is some kind of odd doppleganger named D.B. Davis who is making further developments in his robotics. Finally a time travel device lets him go back in time to where his partners cheated him and lets him sort everything out satisfactorily.