Piper, Paige and Leo struggle to convince Phoebe, now a mermaid, to come back to her life as a Charmed One, when she decides to “”swim”” away from her problems with Cole. Meanwhile, Piper casts a spell to stop her panic attacks but instead of facing her fear, she suppresses it, endangering herself and her baby, when a sea Demon comes after her mermaid sister, Phoebe. In order to help Phoebe, Paige takes drastic measures and enlists the aid of Cole, and his newfound demonic powers.