Partials by Dan Wells

This is by far one of my favorite books, although most books can be said to be so as well. 

Kira Walker, only a medical intern, works with the maternity field, hoping, praying that a baby will not die. Disease has run through the entire population of man kind, ninety nine point nine percent of the population to be exact. They all believe the Partials (warriors that look like men, walk like men, and talk like men) are to blame for this. During the middle of the Partial War was the disease released and they are no longer able to reproduce. Babies die soon after birth and their numbers are decimating. The Senate tries to figure out what to do.

Kira believes that the Partials have something do with this, that they might have a cure for this fatal RM. She decides to capture one with her friends. Of course, the Senate doesn't like this. If word spread out that they had a Partial, they would have a riot on their hands. But still, Kira goes and kidnaps a Partial with the name Samm. 

The Partials need the humans just as much and the humans need them. The Partials are dying. The Partials have expiration dates and they are dying one by one. They cannot reproduce. They're going extinct, just like the humans. Kira agrees to help, but she is now viewed is a traitor for helping this Partial to the Senate. She leaves, goes with her friends to help Samm. But something goes terribly amiss. Information discovered may change Kira's world forever.