If you're unsure whether to check this book out, go get the prelude novella "Unlocked: An oral history of Haden's Syndrome" which is available free online from Tor books. This establishes the setting, a slightly-in-the-future world in which an epidemic has swept the world, leaving huge numbers dead and many more victims of "lock in" syndrome, in which they remain fully conscious but are completely unable to interact with their own bodies in any way.

Since no cure for Haden's Syndrom has been found, the best solution so far has been to create neural network links that allow those "locked in" to control android bodies that allow them to move around the world and interact with people through second hand. "Lock In" itself is set in this environment and is the story of a new FBI agent who is also a Lock In patient using an android body, investigating a murder that may have an impact on the world of the lock in victims and their freedom itself.

It's an interesting world setting, well described, and the characters are likeable and detailed. One interesting thing Scalzi does is to be (I assume) deliberately ambiguous about some aspects of some of the characters, allowing you to make your own assumptions. For example, the race of one character isn't mentioned at all until very late in the book and only in a passing comment, and the gender of another character is never clear at all. Unsure if this is an intentional choice to emphasize the android world that Haden's Syndrome has created, or just a deliberate ambiguity on Scalzi's part to make us check our assumptions, but it made me double take at least once. Overall I think I liked Old Man's War better, but this was still an entertaining story and I'd likely pick up a sequel if there ever is one.