Leo orbs into the living room; Phoebe is so fast that it's hard to keep up with her. Paige tells Leo and Piper that Cole came back just as Phoebe was about to get a default divorce. She didn't tell Piper because of her recent panic attacks. Leo isn't happy that Paige didn't tell him; even though Phoebe told her in confidence, Paige still had a duty to tell her Whitelighter. Piper begins to suffer another attack, and asks if Cole is after her baby. Leo thinks that Phoebe could turn human again if she and Cole declare their love. However, Paige remembers Mylie saying that mermaids' hearts are cold, and thinks Cole may be the reason Phoebe turned into a mermaid.
Necron appears in the Sea Hag's cave and finds the Sea Hag reduced to dust. Phoebe swims in and finds Necron. Phoebe throws several shells at Necron, and Necron blasts her with lightning, drawing blood. She gets caught in a fishing boat and Necron tracks her there. Phoebe fights him off and calls for Leo. Necron sends two ravens to find Phoebe.
Paige is passing off her absence from work as the result of Phoebe being in a bad fishing accident. Leo orbs in; he lost track of her somewhere in the Gulf of Mexico. He thinks she's on the verge of completely turning into a mermaid. Paige has been reading up on mermaids, and on top of that, her first adoption case as a full-fledged social worker is falling apart. Leo thinks he and Piper can handle finding Phoebe alone, but Paige isn't sure if Piper is strong enough mentally.
Leo finds Piper in the attic scribbling spells on the attic wall. She's scared of losing Phoebe, but Leo thinks it's more hormones than anything. Leo tells her to "remove her fear." Piper starts scribbling again.
Paige is at the office trying to save the adoption. Cole shows up at Paige's job. Paige then threatens to orb his testicles far away. Cole argues that doing so would expose magic. Cole offers to help, even though he was fired from the social services agency. Paige pulls him aside and tells him that Phoebe is a mermaid because he broke her heart, and that he needs to disappear.
Piper has written a spell to remove her fear on the wall, and casts it.
Three fishermen unload their catch, and find Phoebe in their net. Just as they're about to kill her, Necron shows up and kills them. He then goes in on Phoebe, but Phoebe whacks him with her tail and knocks him to the ground with a net hook. She calls for Leo, who orbs her out. Necron sends two ravens after her.
Phoebe still wants to be a mermaid, even though Necron is after her. She also has a hunger for water. Piper comes downstairs; she overheard them talking about Necron and is unusually gung-ho about hunting him down. She blows up a picture on the wall that she never really liked, startling everyone. Phoebe wants to go back to the ocean, but Paige won't hear of it. Piper has Paige orb the Book of Shadows downstairs. Phoebe is yearning for water, so Paige puts her in the bathtub.
Cole is trying to help Paige's adoption case go through. He faxed a medical report to the adoption agency, but the spokesman wants the genuine article. Cole waves his hand over the speakerphone, and suddenly the spokesman is willing to take the fax. Darryl walks in; he accuses Cole of killing the fishermen. Cole adamantly denies this, and reminds Darryl that he saved his life the day before. Darryl doesn't like what Cole's obsession with Phoebe is doing to him, and suggests that he go away.
Piper is trying to brew a potion to vanquish Necron, and her lack of fear has made her more reckless than normal; she causes a large explosion in the attic. Paige is alarmed that Piper is taking so many chances, especially since she's pregnant. Leo walks in to check on Piper just as the doorbell rings--it's Phoebe's interview. Leo wonders if Piper had some magical help in overcoming her fear. Paige doesn't believe him until she finds the spell that Piper wrote in chalk.
Phoebe is being interviewed by Nancy O'Dell, who hosts a popular show in San Francisco. Piper suggested they do it in the bathroom, and Phoebe reluctantly goes along. Leo and Paige come down, and are afraid Phoebe could out them all. They also know about Piper's fearless spell. Piper isn't concerned; she thinks she's helping Phoebe to be herself. This isn't enough for Leo and Paige, and they abruptly end the interview. Just as Nancy and her crew are heading out, the ravens land on a branch outside the manor. Necron appears; Paige orbs Phoebe away while Piper blows Necron up. He soon reappears, though, and grabs Piper as he leaves.
Phoebe is out of the tub and spraying herself with a water bottle. Paige thinks the potion Piper was brewing up is too risky to use, and is working on a Power of Three spell. Leo isn't sure if it'll work, since Phoebe is half mermaid and Piper may not let them step in. He also doesn't get why Piper cast the fearless spell, but Paige thinks she felt responsible for turning Phoebe into a mermaid. Phoebe, however, thinks turning into a mermaid is the best thing that's ever happened to her. Paige pulls Cole aside and tells him that she suspects Phoebe might swim away for good once they vanquish Necron. However, she has a hunch that her heart isn't as cold as she thought. Leo starts to orb Paige and Phoebe to the beach, but Paige slips out at the last second.
Necron has tied Piper to a steel rack and is torturing her with electric eels. However, Piper's fearlessness keeps her from feeling the pain. Piper is also, now barefoot.
Paige goes to Cole and tries to convince him to help Phoebe. Paige thinks that Phoebe is still in love with Cole on the basis of her recent advice columns. At last she casts a spell to reveal to Cole how Phoebe really feels, and they learn that Phoebe still loves Cole.
Leo can't find Paige at the manor, and can sense Necron torturing Piper. Phoebe thinks that Necron really wants her, and heads to the cavern to buy more time.
Piper doesn't appear to be shaken up by Necron's torture. Necron is about to feed on Piper's life force when Phoebe appear, offering her immortality in return for Piper's life. Necron cuts Piper down; the force of the landing causes Piper's stomach to bleed. Necron zaps the auger shell onto Phoebe's heart. Paige and Leo orb in and orb the auger shell from Phoebe's heart to Necron's, and then vanquish Necron with a spell. The resulting explosion knocks Piper into the water. Her foot is caught and she is drowning. She sees the ghost of her mother, who counsels her to have faith. She takes her mother's hands and her foot slips free. Leo tries to heal her but the baby heals her first.
Cole teleports Phoebe back onto land. She is upset, of course, but Cole knows how she feels. He asks Phoebe how she truly feels. She doesn't answer, but she becomes human again. She admits to loving Cole but does not want to come back to him.
Paige quits her job at Social Services.
Later that night, Phoebe signs divorce papers while Piper and Leo look at their daughter's baby book. Piper sticks a picture of herself as a child alongside her mother on one page, and Patty magically signs it "Grandma and Mommy."