First off, I'll cover The
Host in novel form, and then move to the movie.
From the book’s cover:
Melanie Stryder
refuses to fade away. The earth has been invaded by a species that take over
the minds of human hosts while leaving their bodies intact. Wanderer, the
invading "soul" who has been given Melanie's body, didn't expect to
find its former tenant refusing to relinquish possession of her mind.
As Melanie fills
Wanderer's thoughts with visions of Jared, a human who still lives in hiding,
Wanderer begins to yearn for a man she's never met. Reluctant allies, Wanderer
and Melanie set off to search for the man they both love.
Featuring one of the
most unusual love triangles in literature, THE HOST is a riveting and
unforgettable novel about the persistence of love and the essence of what it
means to be human.