When a stranger arrives in the seaside town of Bristol Cove, it becomes apparent there was truth in the area's mermaid legends.

Ben finds a strange sound-emitting device on the North Star that could potentially lead him to Chris.

The investigation starts to point towards Ryn; Xander and Calvin find Donna in their search for Chris.

The military facility is on high alert, and while Chris manages to escape, he is not the only one to make it out.

Ben investigates some suspicious overfishing; Decker increases 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 arrives and offers to end the overfishing that threatens the lives of the mermaids in Bristol Cove.