Lewis (Luke Evans) is an outwardly ordinary guy, but in reality he is hiding an obsession - revenge - against Cathy (Kelly Reilly). Lewis kidnaps Cathy in broad daylight and takes her to his home, where he locks her in a soundproof cell and attempt to extract a dark secret from her past.

An adventure-loving couple convince their friends to explore a remote, uncharted cave system in the forests of Northern Australia. With a tropical storm approaching, they abseil into the mouth of the cave, but when the caves start to flood, tensions rise as oxygen levels fall and the friends find themselves trapped. Unknown to them, the storm has also brought in a pack of dangerous and hungry crocodiles.