After her mother's death Cassie Blake moves to Chance Harbor, Washington, to live with her grandmother, Jane. Cassie's life is changed forever when her new classmates tell her that she is a witch, the sixth and final member of their Secret Circle.

Cassie attempts to distance herself from the Circle, even making friends with a non-witch, Sally Matthews. As the witches use their magic more and more recklessly, Diana is convinced they need to bind their powers. This is a problem for Faye, who revels in the increase of the Circle's magic now that Cassie has returned to Chance Harbor. Adam struggles with his feelings for Cassie, while Melissa flirts with Nick. Dawn Chamberlain receives a surprise in the form of her father-in-law, Henry.

Each member of the Circle reacts to the upcoming school dance in a different way. Cassie is asked to go by a classmate, Luke, and accepts after seeing Adam and Diana spending time together. Melissa sees it as an opportunity to get closer to Nick, while Faye has no plans to attend it at all. She prefers to focus on regaining her individual powers, now that the Circle is bound. A man named Zachary Larson has been asking questions about the Circle, causing Dawn to ask Charles to watch over the children.

After the incident with Zachary Larson, Cassie looks up her mother's old friend, Heather Barnes. She discovers Heather has been in a catatonic state since the night of the fire, sixteen years ago. Knowing that Heather was there that night, Cassie decides to use magic to restore Heather, and asks Faye to help — who is willing to do so, for a price. The girls' witchcraft has unforeseen consequences, when a demon that was possessing Heather is unleashed and wants to use the Circle's power.

Cassie struggles with maintaining her loyalties, as she is forced to keep the Circle's secrets from her suspicious grandmother, and Diana tries to maintain hold of her relationship with Adam and arranges a date night. Melissa recruits Nick and Faye to help her find her family's Book of Shadows; however all is not what it seems. The six members of the Circle are brought together in order to fight off a dark force that threatens them from within. Dawn tries to continue making plans for the Circle with Charles, only to discover that he may have more than business on his mind.

Following Nick's death his brother, Jake, returns to town. His presence re-constitutes the Circle, however it is up to Cassie to try to convince the other members to accept him; Jake is a man with a past, and not everyone is as willing to trust him. Jake is not the only newcomer to town, as a witch hunter named Simone poses a threat to the Circle.

It's Halloween and Faye has decided that the Circle needs to have some fun, so she takes it on herself to convince Cassie to throw a party. Faye still has her eyes on wooing Jake back, while a fight with Diana has Adam turning to Cassie, who is trying to make things right with Luke. Meanwhile, the witch hunters have infiltrated the party and plan on doing away with the Circle, once and for all.

After not hearing from Jane for a few days Cassie begins to worry. Diana decides to enlist the Circle, and Jake, to take up the search for Jane, which takes the group to the isolated home of Faye's grandfather, Henry. A storm turns the day trip into an overnight one, and the teens play Truth or Dare to pass the time. Not all is what it seems at the cabin, however, and Faye is forced to confront something dark from her past.

Cassie enlists Jake's help in looking into her father's family, and just why she has powers separate from the Circle. Faye reveals that she suspects that there is more to Jake than he is sharing with the Circle. Adam is torn between his concern for Cassie and his concern for Diana, who has caught the eye of Melissa's cousin, Holden. Dawn and Charles' plans are threatened, as a power shift changes their dynamic.

Cassie learns more about her ancestor, Francis Balcoin, and discovers a secret about herself. She turns to Adam to help her keep this from the rest of the Circle. Diana is thrilled when her grandmother, Kate, comes to town for a visit, who appears to show an unusual interest in Cassie. Still trying to get her powers back, Faye turns to the mysterious Lee LeBeque for help.

Another school dance is upon the Circle, and Adam's father, Ethan, has offered to chaperone it. Cassie and Adam have been investigating her father's past, causing the flame between them to be rekindled. While Adam is ready to move on and embark upon a relationship with her, Cassie is torn between her feelings for him and her friendship with Diana. Faye asks Lee to perform a ritual that will enable her to steal Cassie's individual powers, but it has dangerous consequences that threatens to destroy the entire Circle.

Jake returns to Chance Harbor and warns Cassie that unless she determines just what happened to her father on the night of the fire she, and the Circle, will face the same fate. The two cast a spell to allow them to enter into Jake's memories and return to the night of the fire, however Adam and Diana suspect Jake's motives. Charles and Dawn attempt to outmanoeuvre each other, each trying to get Ethan on their side. Faye's relationship with Lee takes another dangerous turn, as she meets his friend, Callum.

Cassie and Jake meet with a psychic, Lucy, who has information about the medallion found in the previous episode. Cassie calls on the Circle for help unlocking its powers, however Adam worries about the dark magic taking over Cassie. Meanwhile, Ethan has enlisted Diana's help in throwing Adam a birthday party, and Faye and Melissa try Devil's Spirit.

In honor of the holiday Faye throws a girls-only, "anti-Valentine's Day" slumber party at her house, and the other (female) members of the Circle are invited to attend. The night takes unexpected turns as both Melissa and Diana use Devil's Spirit to get high, and Lee crashes the party to help Faye increase her power. Meanwhile, Cassie turns to Jake and Adam for help after the spirits of vengeful witches begin to haunt her.

John Blackwell, Cassie's father, shows up on her doorstep; however surprise turns to suspicion when he wants the medallion. Eben and his band of witch hunters take Cassie captive, causing Jake to offer a trade and Adam to call the other Circle members for help. Meanwhile, Faye and Diana are both concerned that Melissa is spending too much time in the company of Callum.

Cassie catches Blackwell sneaking around the abandoned house, leading Adam to believe that he is looking for a device to drain witches' powers and is still consumed by his dark magic. Faye meets Eva, and is taken aback to discover that she is Lee's girlfriend. Meanwhile, Melissa encourages Diana to date a mortal guy, specifically a handsome Australian, named Grant, who is new to town. Also, Dawn has a reunion with Blackwell, but it isn't entirely what she expects.

Blackwell tells Cassie and Adam that while their love might be destined, it is also cursed; once awakened a member of the Circle will die. It is a race against the clock to find a way to break the curse before it takes Jake's life. Meanwhile, Faye becomes certain that Eva is hiding something once it becomes apparent that Lee is missing, and Charles plots against Blackwell.

Witch hunter Samuel comes to town with a message for Blackwell about Eben's plans; he is trying to resurrect the demons that Blackwell summoned to Chance Harbor sixteen years ago, and plans on making a human sacrifice. Meanwhile, Diana continues her relationship with Grant, but it is revealed that her magic is not the only secret in their relationship. Faye and Melissa compete for the attention of a jock at the Boathouse, while Adam tries to deal with no longer remembering why he loved Cassie.

To protect themselves from the witch hunters, Jake, Cassie and Faye team up to seek out Jake's grandfather, Royce, to find his family's crystal and are confronted with disturbing theories about the events of sixteen years ago. Meanwhile, Diana tries to balance her pursuit of the Glaser crystal with Melissa and Adam with her new romantic life with Grant, who demands to know what she's hiding. At the same time, Callum attempts to re-insert himself into Melissa's life. Also, Charles and Jane plot their move against Blackwell and it is revealed that Diana is the other Blackwell child. Then Blackwell reveals his dark powers are still intact and he wants to use them to create a black magic Circle with his newly found kids.

When a crystal is magically stolen from the abandoned house, the Circle decides it was the traitor witch working with Eben. Jake calls for a meeting with Isaac to see if they can get him to change sides, only to find out that Isaac has been killed by Eben. Cassie’s loose grasp on her dark magic threatens to destroy any possible alliance when their pursuit of the traitor leads them to the “Creepiest Place on Earth.” Meanwhile, Faye and Jake work together to steal Dawn’s crystal, Melissa and Adam pair up and uncover a new magic trick, and a frustrated Diana reaches out to Charles for help. Diana and Cassie chase the traitor in the “Creepiest Place on Earth” and Cassie uses dark magic to stop him only to find out it's Nick who is supposed to be dead.

It’s Prom night in Chance Harbor and after Adam uncloaks a crystal hidden in the school, Blackwell tells Cassie she can use her dark magic to find it. When Cassie follows this advice, it leads her to a dangerous discovery. Meanwhile, Faye invites Jake to Prom, despite the fact that he stood her up two years earlier. Adam, Diana, Cassie and Melissa finally make it to Prom but when they lose the crystal to Eben, they end up in a life and death situation. Meanwhile, Dawn attempts to stop Blackwell, who casts a deadly spell on Charles.

When Faye is captured by the Witch Hunters, Jake, Melissa and Adam set out to save her. Blackwell wants to unleash the power of the crystal skull and tries to convince Cassie and Diana that their Balcoin blood is the only way to stop the Witch Hunters permanently. Meanwhile, Dawn and Charles discover a way to get their powers back ... but one which comes at a very big cost.