When Caleb discovers that Blunk took the key he was suppose to leave behind in Meridian for Vathek, the girls return to Meridian to return the key before Cedric and Phobos discover Vathek is a spy for the rebel army.

It's Will's birthday party and if there's one thing she doesn't want, it's a party. The girls manage to throw one anyway and everything is going swimmingly until one of those Meridian fang-faces shows at City Hall looking for birth certificates for a certain teenage girl. Apparently, the current Prince of Meridian has a long lost sister...

While helping out in Community Service Day, Will and Hay Lin find a strange Meridian graffiti which The Mage identifies as belonging to a Beast, living in Heatherfield in human form. Will suspects her History teacher, Professor Collins, and the girls immediately formulate a plot to force the suspected monster into revealing his true form.

Every student in Sheffield Institute is getting his midterms back and everybody is just about happy with his grades, except Taranee. Cedric's disguise as a bookseller seems to have attracted Cornelia, Elyon, Irma, Taranee, and Hay Lin to the store to look for history books (and to ogle at Cedric). While in the bookstore, the W.I.T.C.H. girls inadvertently touch an inversion point and find themselves in the middle of a Labyrinth inside Phobos’ castle. Will they be able to find their way back without powers and without help from their leader Will who is at home buried in school work?

The W.I.T.C.H. girls go on a school skiing trip to show up Swiss exchange-student vamp Sondra, who seems to have mesmerized all the boys at Sheffield. Little do they know that Phobos wants to take advantage of this trip to divide them and separate the other four Guardians from Will and the Heart of Kandrakhar, the only thing that can activate their full powers.

Tired of having their supply lines constantly ambushed by the rebels, Phobos and Cedric start a rumor that the Seal of Phobos has been found in order to flush out the spy. The seal of Phobos is an artifact much like the Heart of Candracar in that it can open up places like the Infinite City or The Veil. Caleb, who is stuck on Earth after trying to use a portal without telling the Guardians where it is, hears the false rumor and falls for it, eventually getting captured by a living quicksand pit at Torus Filney. Meanwhile, the girls are faced with the prospect of having to perform a play based on a myth of their choice thanks to Hay Lin's non-consentual group sign-up. The girls choose the origin story of the Heart and subsequently their powers but before the curtain can go up, Grandma tells them about Caleb's disappearance and capture. Stuck for a plan of action, the girls are enlightened to another of the Heart's powers: the ability to clone the Guardians. While the clones put on a miserable and detention-provoking performance, the girls save Caleb and everyone else who has been captured by the quicksand monster and make sure no one falls victim to it again. The good news is that Phobos really doesn't have the seal. The bad news is the Seal is lying in a storm drain in Meridian, waiting for some poor schmuck to find. As the episode closes, Cedric demands a list of all who left the castle yesterday.

While at the Art Museum trying to capture the feeling of the middle ages for their school carnival, Will, Taranee, Cornelia, and Hay Lin get sucked into the painting they are studying. Unbeknowst to the girls, Phobos knows they are trapped in the painting and sends Frost the Hunter after them, but the girls escape with the help of Elias Van Daal, the imprisoned artist of the painting. Meanwhile, Irma, Caleb and Blunk have to stall for time at the Medieval Carnival and figure out how to get the girls back to Heatherfield. Anachronistic hell breaks loose when Cedric and his goon platoon enter the painting to get the Heart of Candrecar and girls have to paint like mad to get away. Irma and Caleb rescue the girls from the painting and manage to salvage the school carnival thanks to the number of people they brought back with them from the painting.

Phobos has finally found an indisputable way to find his long-lost sister: The Star of Threbe. Back in our world, The Silver Dragon (Hay-Lin's family business) is threatened when Blunk stinks up the joint with his new ""home"": a garbage dumpster. While the girls try to give Blunk a much needed bath, Cedric places the Star in his window shop and Cornelia's platinum-haired friend walks in and takes it. Now when the girls try to change back, they find themselves stuck in Guardian form and powerless. Not knowing what to do, the girls race back to the Silver Dragon to enlist Mrs. Lin's and Caleb's assistance. In the meantime, Cedric sends a monster plant to Earth to tie up the Guardians while he makes contact with the Princess. The girls are forced to fight without their powers until the Princess returns the Star to Cedric, which leads the girls back to their powers. Unfortunately, Phobos and Cedric have who they're looking for, she just doesn't know it yet.

Elyon is Phobos's sister and the true heir to the throne of Meridian, she just doesn't know it yet. Vathek overhears Phobos and Cedric's plans for capturing her and hurries to tell Caleb only to end up running for his life when Cedric comes to stop him. Vathek and Blunk escape to Earth with Cedric and a worm-looking monster hot on their heels. Vathek relates the news to Caleb who relates the news to the Guardians and they go after Elyon to keep her safe from Cedric's clutches, however, they have to hold off the Larvek from eating Vathek and Elyon slips off in a bad mood after her new beau gives her the heave-ho. She heads back to her place of comfort: Cedric's bookshop.

Phobos is preparing the Ritual of Amalgamation. He needs symbols of Elyon's body, mind, and spirit. Cedric takes her hairbrush, A+ math test, and is trying to take her breath. Meanwhile, Martin catches a glimpse of a Hermeneuta beast from Meridian and the only thing that will get him away long enough for the girls to send it back home is a date with Irma. Catching the little beast is not as easy as it sounds, especially when the mom shows up. In the end, Cedric finally captures Elyon's breath in a balloon and all that's left is to take her to Meridian.

It's parents' night at the school, and nobody (except Hay Lin) seems very excited, especially Elyon. She feels that Cedric is the only one who understands her, not her friends, and especially not her family. When Elyon does her family tree research, her parents do not have any pictures of her other relatives. Elyon thinks that it's because they don't care about her but it's for a whole other reason. Cedric reveals to Elyon, that her parents are beasts, and that she is the Princess of Meridian. Elyon is so confused but she goes to Meridian, her original home.

Elyon seems to have adjusted to her new life as the Princess of Meridian, living in Phobos' castle, although she is still under the illusion that Phobos has created. Meanwhile, Cornelia gets so upset about losing Elyon to Cedric and Phobos that she quits being the Earth Guardian. Phobos uses this to his advantage and changes the image in the sand to make it look as if Cornelia is getting along just fine with the others and not missing Elyon at all. Phobos sends Meridian Mudslugs after the remaining Guardians and without the Earth Guardian. When they realize that Cornelia is the only one who can defeat them, Will uses the Heart of Kandrakhar to tap into the broadcast frequencies to reach her. Cornelia saves the day by telekinetically levitating the huge mudslug near the portal. She is now officially back in the W.I.T.C.H. group.

Will and the rest of the girls try to tell Elyon the truth about Phobos and Meridian, but that becomes very hard when Phobos teaches his sister to make ghostly images of herself to confuse her former friends and the rebels. The real Elyon is upset that she didn’t bring her sketchbook from Earth so Phobos sends Lurdens through a portal to her old bedroom to fetch it. But the creatures also trash a stash of chocolate, the scent from which Blunk is able to follow to Phobos’s and Elyon’s secret Meridian mountain hideout. The Guardians and Caleb search for Elyon under the mountain but are ambushed by Lurdens. Forced into the open, they battle Cedric on the mountainside before returning to Earth, no closer to warning Elyon of the terrible danger she’s in.

Phobos sends shapeshifting monsters into Meridian to pose as and discredit the Guardians so Elyon will lose what little trust she has left in her friends. While the real Guardians do battle with the evil twins, Cornelia and Caleb try to persuade Elyon that Phobos only wants her for her power, but she won't listen. Caleb, however, does something to shake Elyon's faith in her new brother: he bows to her. Unnerved by this, Elyon is starting to suspect that Phobos is not telling her everything.

Cedric uses a magic horn called the Horn of Hypnos to make everyone who hears it into obedient zombies called trancemarchers. Unfortunately, Guardians of the Veil, namely Hay Lin, are no more immune to its effects than anyone else. How are the girls going to break Cedric's hold on their friend and what is being done about Phobos' Book of Secrets that Caleb swiped from their last trip into Meridian?

Phobos uses the knowledge of Caleb's father's being alive to lure him and the Guardians to the Underwater Mines for an ambush. Fortunately, Hay Lin hears the guards whisperings, which allows the group's unimpeded access to the mines. However, the element of surprise is soon lost and the group is on the move. Cedric floods the mine and sends the group plus Caleb's dad on an Indiana Jones-type mine cart ride to the main shaft. Once there, they use the guardroom to float to the surface and come face-to-lizard face with Cedric and a platoon of guards. Cedric tries to go after Caleb and the miners stranded in the remains of the guardroom, but Irma and Hay Lin cool Cedric out with a flash-frozen bubble. Phobos is sitting pretty in his castle, thinking that he has taken care of the major thorns in his side until the girls show up with the last laugh in his looking-glass floor.

The Guardians are stunned to learn that their math teacher Mrs. Rudolph is the Meridianite nanny who brought Elyon to Earth twelve years ago. She opened a portal with the Seal Of Phobos... but lost it during the escape. On the run from castle guards, Caleb and Blunk split up. Blunk hides in a sewer where he finds The Seal where it has lain undiscovered for twelve years. Not knowing what he has, Blunk begins waving the Seal around, opening portals all over Heatherfield, which the Guardians rush to close. But the girls don’t realize that every time they do, they’re cutting off an escape route Caleb needs to avoid capture. When the Seal of Phobos encounters the Heart of Candrakar the two amulets battle and the Heart ends up absorbing the talisman and all its powers. Thus empowered, the Guardians are able to help Caleb escape from the work-yard in Hoogong Gorge. Back in Heatherfield the group uses the Seal to open The Book of Secrets, revealing for the first time Phobos’s plan for draining his unsuspecting sister’s powers and turning her into a Whisperer, imprisoned within a Black Rose forever.

Elyon misses her parents and Phobos agrees to let them visit Elyon. However, when the guardians find out that Elyon's parents are held captive in the Cavigor prison, they go in and try to bust them out. But the task is easier said than done when Elyon's parents have been hypnotized, with the addition of hundreds of guard led by Cedric chasing them and the task of freeing hundred of prisoners. In the end, they free everybody including Elyon's parents, which makes Elyon worry about what the rebels will do to them.

When Caleb's best friend, Aldarn, accidently becomes hypnotized by Elyon into signing a peace treaty, Caleb has to fight him for the position of leader. Meanwhile, after leaving their baking duties for the school bake sale to Blunk, the guardians enter a trap filled with Larveks and they must defeat them before the rebels get eaten by them.

Cedric blocks the village’s water source, in the hopes that thirsty Meridianites will break down and reveal the location of the rebels’ secret hideout. There’s fresh water in a nearby lake but it’s inhabited by an elusive creature called the Kaithim, which the Guardians have to battle. But Cedric discovers the entrance to the Infinite City, just before Vathek is able to seal his comrades inside. Aldarn, separated from Caleb and with limited food before the City is inevitably overtaken, makes a tactical decision to charge the Castle. Caleb and the Guardians join the premature attack but the uprising fails and many rebels, including Aldarn and Caleb’s father, are thrown in Phobos’s dungeons

Caleb is making plans for the escape of the rebels captured by Phobos in the abortive battle of the Meridian Plains . With Blunk’s help, he tries to map the tunnel system to the castle’s dungeon. But the reconnaissance mission goes wrong and Blunk is left behind on Meridian. Looking for the Passling, Caleb and the Guardians find and save a Castle Guard wounded in battle and left for dead by Cedric. When the Guard, Tynar, sees Earth and the girls’ concern for his recovery, he switches loyalties and promises to guide them through the complex subterranean passageways into the dungeons where the rebels from the uprising are being held. The daring raid frees the rebels, and Tynar begins spreading the word among Phobos’s guards that the other side of the Veil is not as they’ve been told. Back in Heatherfield, Will impulsively kisses Matt, who has offered her a pet dormouse named Mr Huggles earlier in the episode.

In Meridian, the Infinite City occupied by Phobos' guards leaves a thousand rebels with nowhere to hide while Elyon, though shaken by the sight of monstrous Lurdens working in her castle, is still blissfully unaware of what’s being planned for her Coronation. Caleb and the Guardians have to get close enough to warn her, but how can they without the Heart of Kandrakhar which has been stolen by Jeek the evil Passling?

In Meridian, Elyon is at the apogee of her powers and excitedly prepares for tomorrow’s Coronation. But Phobos and Cedric talk out of her earshot: there’s something afoot that Phobos isn’t telling his sister. Meanwhile in Heatherfield, Caleb has finally figured out with the Guardians’ help a way to get his men across the Meridian Plains unseen. The final battle is about to begin.