After the world is in ruins, due to a man-made plague, a battle of Biblical proportions ensues between the survivors.

Sam has a premonition in which a man is killed, but the murder is made to look like a suicide. Sam convinces Dean that they must investigate the case, but…

Donna comes ashore with two other members of her colony to bring Ryn back home. When mermaids once again begin wreaking havoc throughout the town, Dale tries to put an…