I've really become a fan of Michael Crichton books. I appreciate that he takes the time to make the science in his books credible. This time, a US corporation, using quantum mechanics, achieves time travel. It has problems, of course. The book raises the expected questions about the hazards of time travel and potentially changing history, although the answer is a little different that what you find in other books tackling time travel. Overall, a fun and entertaining read.