Peter Watts - Blindsight
Free ebook from here:
http://www.rifters.com/real/Blindsight.htm
"Canadian author Watts (Starfish) explores the nature of consciousness in this stimulating hard SF novel, which combines riveting action with a fascinating alien environment. In the late 21st century, when something alien is discovered beyond the edge of the solar system, the spaceship Theseus sets out to make contact. Led by an enigmatic AI and a genetically engineered vampire, the crew includes a biologist who's more machine than human, a linguist with surgically induced multiple personality disorder, a professional soldier who's a pacifist, and Siri Keeton, a man with only half a brain. Keeton is virtually incapable of empathy, but he has a savant's ability to model and predict the actions of others without understanding them. Once the Theseus arrives at the gigantic and hideously dangerous alien artifact"
Caution! Not for the faint at heart....
The blurb is from Amazon and the rest of it contains spoilers so I cut it short.