The coastal town of Bristol Cove, known for its legend of once being home to mermaids, is turned upside down when a mysterious young woman appears and begins wreaking havoc upon the small fishing town to look for her captured sister who was abducted at the hands of the local military. Marine biologists Ben and Maddie work together to find out who and what drove this primal hunter of the deep sea to land.
In the series premiere, a mysterious girl arrives in a small coastal town, leading to the return of vicious mermaids who are seeking to reclaim their rule over the ocean.
Ben and crew of The North Star uncover a device emitting a strange sound. Meanwhile, Ryn finds shelter in the home of the local folklore expert.
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.
When the military facility goes on high alert, Chris manages to escape, but he’s not the only one who gets out.
Ben begins to investigate some suspicious overfishing, meanwhile Decker ramps up his efforts to find his escaped mermaid and shows the true extent of his influence.
When Ben and Maddie attend his mother’s fundraising gala, an unexpected guest shows up and offers to put an end to the overfishing that’s threatening the lives of the mermaids in Bristol Cove.
When Ryn is taken in for questioning, Maddie rushes to her rescue. Meanwhile, Ben and Xander return to the deep sea to search for answers, only to be met by an uninvited guest.
Bristol Cove mourns a loss causing Ryn to experience a new human emotion.
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.
With more mermaids landing at Bristol Cove’s shores, the threat of discovery increases. After his encounter with the siren song, Ben tries to cope with the after effects. Maddie’s mom returns to town and tries to connect with her daughter. Meanwhile, Ryn attempts to adapt to life on land.
Ben, Maddie and Ryn desperately try and keep the newly arrived mermaid pack hidden from the rest of the town, but the new mermaids’ quick degradation on land forces them to get them back to the sea unnoticed during the town’s Mermaid Beauty Contest. Elaine grows more suspicious of Helen and her connections to their family.
Ryn fights to maintain leadership of the pack when her loyalties are questioned over her friendship with Ben and Maddie. Ben interferes in a mermaid ritual and Helen discovers more about her family lineage.