This summary is off of Stephenie's website:
The basic premise: The Host takes place after a bodysnatchers-style invasion of the earth. We (the humans) lost. Our narrator is Wanderer, one of the invading "souls," who struggles to navigate all the bewildering challenges that come with living inside a human body. She was forewarned about these challenges—the overwhelming emotions, the stunning physical responses, the glut of senses, the too vivid dreams and memories… However, there was one challenge Wanderer didn't expect: the former tenant of her body, human survivor Melanie Stryder, refuses to fade away into oblivion the way she should. Melanie lingers as an angry presence in Wanderer's head, holding on to her human secrets and filling Wanderer's thoughts with visions of the man Melanie loves—Jared, another human who still lives in hiding. Unable to separate herself from her body's desires, Wanderer yearns for the man she's never met. Outside forces combine to make Wanderer and Melanie unwilling allies, and, working together, they set off to search for the man they both love. It's possibly the first love triangle that only involves two bodies.
It sounds a little confusing but definitly very interesting. Even though it's not Breaking Dawn I'm really looking foward to reading this new novel from Stephenie Meyer.