Piper and Leo are remodeling their bedroom closet to turn it into a nursery for the baby Piper is expecting. Piper comes across the baby book that Patty had made for her. The first few pages are full of pictures and mementos, but the rest of the book is blank. Patty never had a chance to finish the book because she died while Piper was just a little girl.
Meanwhile, the Sea Hag is in her lair with a beautiful mermaid named Mylie. The Sea Hag has given the mermaid legs so she can find true love with a mortal man. But there's a down side to the deal: Mylie's boyfriend must confess his love, or Mylie must give the Sea Hag her immortal soul.
"It's too bad, Mylie," the Sea Hag says, "but your time is up. You had thirty days to find love or the penalty would be death."
"But he does love me, I know he does."
"Oh, really? Did he tell you?"
Mylie is defiant. "He doesn't have to tell me he loves me."
"Well, actually," the Sea Hag says, "he does."
Mylie refuses to give in, and she swims away. The Sea Hag conjures the elements to track Mylie, bringing a storm of mythical proportions to San Francisco.
Mylie finds Craig, her boyfriend, just hours before he's scheduled to board a plane on a business trip. She tells him she can't explain, but she needs him to tell her how he feels about her. Before he can reveal what's in his heart, a drop of rain falls on Mylie's leg, and the little patch of skin turns to scales. She runs off to escape the storm.
Paige's boss, Mr. Cowan, tells her he's promoting her to social worker. She calls Phoebe to share the news. But Phoebe has news of her own: She's got an appointment that afternoon with a judge about her divorce decree.
Phoebe heads to the parking garage, where Mylie approaches and tells Phoebe she needs magical help. A car drives by, splashing water onto Mylie, and she turns back into a mermaid.
"We need to go!" Mylie says. "The Sea Hag will track my tail!"
Phoebe helps Mylie into the car. The Sea Hag appears, but Phoebe drives through her. The Sea Hag dissolves into a puddle of water but transforms back to herself again.
At the manor, Paige comes home to help but finds Phoebe fixated on her court date, while Piper is looking for ways to avoid a battle with the Sea Hag. The sisters agree that the best course of action is to save Mylie's life by convincing Craig to confess his love. Phoebe goes to her court date, while Paige goes to the airport to find Craig.
At the Sea Hag's lair, a skeletal being called Necron has come looking for Mylie's soul, which the Sea Hag had promised him. The Sea Hag convinces him she needs more time. Necron says that he'll be back—and if he isn't able to feed on the mermaid's immortality, then he'll feed on the Sea Hag's life force.
Paige finds Craig and convinces him that Mylie needs him. He misses his flight to go back to the manor with Paige.
"Paige told me your life was in danger," Craig says to Mylie. "What's going on?"
Mylie looks at him intently. "I really need to know how you feel about me."
"I can't believe we're back on this!" Craig is disgusted, looking at Paige and Piper. "Are you two in on this joke or what?"
"It's no joke," Paige says. "You have to tell her how you feel about her. Her life depends on it."
"What is this?" Craig asks. "The delusional girls club?"
Mylie realizes the only way to explain the situation to Craig is to show him. She sits on a chair and pours water on her legs; they transform into a mermaid's tail. Craig, horrified runs out.
The next moment, the Sea Hag appears. Piper tries to freeze her without success. The Sea Hag traps Paige in a cascade of water. Piper, terrified, hides behind the couch; the Sea Hag reminds Piper of the water demon who killed her mother. Piper worries that like her mother, she'll die before she can raise the child she's carrying.
Phoebe, meanwhile, is in the judge's chambers. Darryl is at her side. Phoebe tells the judge that she's made every effort to locate her husband, but he's simply disappeared. Darryl supports her claim, saying, "It's my belief that Mr. Turner has left the country."
Phoebe is about to sign the divorce papers when Cole's voice is heard. "Is this the right office?"
Phoebe and Darryl confront him outside the judge's chambers. Cole, frustrated, turns Darryl into a water cooler. "Too many people talking at once," Cole says.
"You see, Cole, this is exactly what I'm talking about," Phoebe says. "Good people don't turn other people into water coolers."
Cole insists that he can be good, but Phoebe wants nothing to do with him. She picks up a letter opener to fend him off. She slices his hand; it magically heals, but his blood sizzles on the letter opener.
Phoebe returns to the manor to learn that the Sea Hag has captured Mylie. Paige writes a power-of-three spell to locate the Sea Hag. It has a side effect, however; it turns Phoebe into a mermaid.
Darryl is involved in a shootout when Cole appears and freezes the gunman, saving Darryl's life. Cole helps Darryl cuff the bad guy, then says, "Don't forget to tell Phoebe what I did."
At the Sea Hag's lair, Mylie is despondent over Craig's rejection. She decides she can't spend an eternity pining away for love, so she agrees to give the Sea Hag her immortality. The Sea Hag places an auger shell over Mylie's heart, which will draw out her immortality.
Mermaid Phoebe finds the Sea Hag's lair. She calls Leo, and he tries to orb Piper and Paige to Phoebe. But at the last moment, a terrified Piper lets go of his hand and stays behind.
When Leo and Paige arrive at the lair, Paige calls for the augur shell but drops it into the water when the Sea Hag entwines her with seaweed. Phoebe picks up the shell and throws it at the Sea Hag. The augur shell draws out her life force, and the Sea Hag turns to dust.
Mylie, however, is near death. Leo can't heal her because she isn't human. He orbs to Craig and brings him to the lair. When Craig sees that Mylie is dying, he finally confesses his love, turning her human. Leo heals Mylie. When Mylie sees Craig, she smiles, and they kiss.
But Phoebe, still a mermaid, swims off, lured by the call of the sea…
TO BE CONTINUED