The Host by Stephanie Meyer

In The Host, Stephanie Meyer tells the story of Wanderer, a Soul whose race survives by traveling from planet to planet and taking over the bodies of the inhabitants. When the Souls come to Earth, Wanderer is placed in the body of Melanie, who refuses to lose her consciousness. For the first time, Wanderer’s race of Souls seems to be succumbing to the habits and emotions of the race that they are taking over, becoming more human. Told in first person narrative by Wanderer with insertions by Melanie, the story describes a world in which humanity is infectious and the definition of what is right and what is wrong can change.