Trailer for the cult horror Possession.
A secret agent named Marc returns home after an assignment to find his wife Helen acting peculiar. He soon realizes that she's been having an affair. But it turns out that Helen has been busy in more ways than one: she's created a monster-- literally--from the evil within her. And the slimy creature, despite being held in captivity by Helen, has violently killed a number of people. Now, Marc must forgive Helen's indiscretions in order to save her from the being, which could escape at any time.