Piper, Phoebe and Paige come to the aid of Mylie, a Mermaid-turned-human, when she shows up looking for their help after a pact she made with an evil Sea Hag begins to go drastically wrong. Meanwhile, Phoebe attempts to divorce Cole, until he shows up claiming to want her back, Paige, attempts to juggle her new position as a full fledged Social Worker, as well as being a Charmed One, and Piper must protect her unborn baby, and face her fear of water.

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.

Cole and Phoebe both fall under the spell of the Siren, who lures husbands to her and entrances their wives to follow with the intent to kill, leaving Piper and Paige to figure out how to save Phoebe. Piper, upset with Leo because he does not understand the challenges of being pregnant, and Leo, frustrated that Piper does not realize the demands of being a Whitelighter, have their personas switched magically by their unborn child.

When a demon coerces a boy into turning him into an evil comic book villain so he can steal an Elder's powers, the boy transforms The Charmed Ones into comic book heroes with superhuman strengths to prevent this from happening.

While seeking the advice of a fortune teller regarding her missing power of premonition, Phoebe discovers that there is a demon who has been stealing the eyes of Gypsies. Meanwhile, Piper wants to see a doctor about her baby, but Leo is concerned about the threat of exposure.

Barbas, the Demon of Fear, returns and tricks Paige into giving him Cole's powers, and plots revenge on the Halliwell sisters by playing them against their darkest fears.

When Phoebe must constantly save the life of her new boyfriend, a warlock shows up from the future, claiming that future Cole sent him in order to kill the boyfriend before Phoebe's dies instead. However, present Cole cannot allow this and tries to help the sisters protect Miles, but when the warlock decides to work on his own agenda, by stealing the Book of Shadows, it results in the death of two of the Halliwell sisters. The survivor must decide whether going back to change the past is the right thing to do.

Paige gets to know the Whitelighter in her, when she meets her first charge, a man named Sam, unbeknownst to her is actually her real father. Meanwhile Cole tries every possible way to get himself vanquished by the Charmed Ones. Piper and Leo have problems in finding a magical creature that does the babysitting part, and things go bad to worse when they're poisoned by a Darklighter, leaving Sam as the only one who can save them.

Phoebe falls prey to Jeric, a demon in search of the perfect body to hold the spirit of Isis, his dead lover. To trap the spirit, Jeric mummifies Phoebe's body. Meanwhile, Cole tries to save Phoebe by making a deal with the demon.

After kidnapping Phoebe, Cole sends a shapeshifter to assume Phoebe's identity to help him manipulate Piper and Paige into giving him ownership of the Manor, allowing him access to the powerful Nexus located beneath the house. Meanwhile, Phoebe plans her escape, and Cole gets Paige arrested and ensures that Piper's club fails to pass health inspections in order to keep them distracted.

In his twisted attempt to win Phoebe's heart back, Cole casts a spell that alters reality, that eliminates Paige as a Halliwell and destroys the Power of Three. Meanwhile, Paige suddenly finds that her sisters have no knowledge of her existence and that past villians have come back to haunt them.

Glen returns to Paige's life with a big surprise - he is about to get married to a girl called Jessica. Meanwhile, the sisters summon a Witch Doctor whom they want to dispatch all the evil remnants that surround the Manor.

A demon attacks The Charmed Ones with dream dust, causing their nightmares to come to life. Paige is harassed by an evil clown at a baby shower, Piper has an affair and Phoebe is chased by a maniac with a chainsaw. The sisters must use magic to put themselves to sleep to re-enter their nightmares and unmask the symbolic meaning of their dreams.

Phoebe and Paige go to a summit meeting with the leaders of evil and discover that all magic - both good and bad - has disappeared enabling the leaders to steal Piper's about-to-be-born baby and welcome the twice-blessed child into the kingdom of evil.

The Charmed Ones must protect Piper's son from two demons, but the baby has a few surprises of his own. Meanwhile, Paige goes undercover as a bounty hunter and Phoebe's future with the newspaper is threatened by the new owner.

The Charmed Ones face a demon who has been killing Leprechauns and stealing their magic but when the Leprechauns endow the sisters with good luck, which enables Paige to gain material wealth, Phoebe to meet a man, and Piper to book a major star to play P3, plans backfire.

When Piper and Leo begin to have marital problems, Piper casts a spell to allow them to literally see their past together. However, the spell goes awry when Phoebe and Paige are sent back in time to relive Piper's memories, and a warlock bent on destroying the Charmed Ones tags along for the ride.

When a demon attacks and kills one of the three nympths that protect a lake, the Charmed ones try to help. However, once the demon is destroyed, the nypmphs decide Paige should replace the fallen nymph, and they won't take no for an answer.

In order to get close to baby Wyatt, the Crone steals one of the senses from each of The Charmed Ones, in an attempt to fool the child.

When Grams comes to the manor for a Wiccan birthing ceremony, for Wyatt, the sisters find out that she has brought a memory from her past, a former lover who wants to kill the Charmed Ones and bring back the love they once shared. Meanwhile, Phoebe contemplates Jason's invitation, even though it will take her away from her family, and Paige casts a truth spell to figure out if Nate can accept her being a witch.

When the mythic Gods, the Titans, are released and kill all the elders, Leo is forced to take over. Meanwhile, a mysterious Whitelighter from the future guides the Charmed Ones when Leo gives the girls the ultimate power to vanquish the Titans, recreating them as Greek Goddesses, despite the risk that they will be seduced by their vast new powers.

Now all powerful Greek goddesses, the Charmed Ones must try to not be seduced by their new powers and stay focused on vanquishing the Titans before they destroy all the whitelighters. Meanwhile, Leo must decide whether to become an elder or stay with Piper & Wyatt.