A drifter (Shea Whigham) kills a traveling preacher and takes his place at a small-town church, but the police chief (Michael Shannon) suspects foul play.

Siren II, a submarine under the command of Capt. Phillips, ventures into the deep on a mission to recover the missing Siren I. Their quest is hindered when the submarine becomes entangled in a patch of toxic seaweed.

In Chile, a group of travelers who are in an underground nightclub when a massive earthquake hits quickly learn that reaching the surface is just the beginning of their nightmare.