As an old friend visits Helen, a new mermaid arrives leaving Ryn questioning their motives; Maddie learns the truth behind Ian's death; Ben fights for his mother's treatments; Xander is inspired to take on more responsibility.
When another mysterious death is uncovered in Bristol Cove, Ryn suspects Tia; Maddie befriends a new acquaintance in Seattle; Helen warns the hybrids of trouble; Xander begins training; Ted revisits the past.