Dale and the local police’s investigation starts pointing directly to Ryn, meanwhile Xander and Calvin’s search for Chris heats up when they locate the nurse who works at the military bunker.

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 end to it once and for all.

In the season finale, the enchanting siren song takes hold of Ben and Decker. Meanwhile, Dale must answer for the escalating crime in Bristol Cove.

Dale copes with the fallout from Maddie and Ryn’s encounter with the man from Susan’s past, while Katrina continues to persuade the rest of the mermaid pack to get on her side—even if that means brute force against both mermaids and humans.

Ben faces a choice that has rippling consequences amongst mermaid, hybrid and human alike, as the truth about mermaids is exposed.