Cassandra 'Cassie' Blake is the heroine, protagonist and the main female lead character of The Secret Circle trilogy. She was born on July 23, 1976 in California. In the television series, her mother, Amelia Blake, is deceased. In the novels, Cassie's mother, Alexandra Blake, is still alive and makes the decision to move the two of them to New Salem. Cassie is the love interest, ultimate soulmate and significant other of Adam Conant.

Physically, Cassie is described to be beautiful and the girl next door with soft, slightly wavy blonde and clear blue-silver eyes. Personality wise, Cassie is described as being shy, unique, loner, withdrawn and quiet but she becomes significantly more "alive" and opens up after she unexpectedly meets Adam. Cassie loves listening to music and collecting unicorns. She loves Phantom Of The Opera and greatly enjoys creative writing.

While on vacation in Cape Cod, Massachusetts she meets the young, handsome and mysterious Adam, whom she saves from a group witch hunters. Cassie feels an immediate, magnetic, intense and indescribable attraction and connection to Adam. She also realizes that she and Adam are bound together by the silver cord of destiny or fate, which implies that Adam and Cassie are destined and fated to be together and that they are ultimate soulmates. He then leaves Cassie, giving a token of friendship.

Cassie arrives at her vacation home that evening to find out that she and her mom are going to have to live with Cassie's sick grandmother in New Salem. Once they arrive in New Salem, Cassie finds out that she will be going to the high school there.

Settling in in the town of New Salem, Cassie eventually befriends Nick Armstrong, Faye Chamberlain, Deborah Armstrong, Sean Dulany, Melanie Glaser, Chris Henderson, Doug Henderson, Laurel Quincy and Susan Whitler; all members of the Secret Circle coven. She is also friends with Jeffrey Lovegood and Sally Waltman. Upon her arrival at New Salem High, she witnesses an altercation between a girl named Faye Chamberlain and Sally Waltman. After this occurrence, Faye and her friends Deborah and Suzan constantly pick on Cassie and will not leave her alone.

At the end of her first week, Faye, Suzan, and Deborah lure her into the old science building and torture her with fire, at which point Diana Meade comes rushing to the rescue and becomes Cassie's best friend and adopted big sister. Cassie then starts hanging out with the popular, mysterious club. A couple of weeks later, Kori Henderson is killed and the club initiates Cassie instead, who finds out the club is a coven of witches. She is then initiated into the coven of witches. After the ceremony, Adam arrives, who happens to be her newfound friend Diana's longtime boyfriend.

After seeing Adam, Cassie makes a blood promise to herself that she won't let anybody discover her deep, strong and intense feelings for Adam. Adam comes with news that he has found a master tool. He takes out the crystal skull. Faye demands that the crystal be used immediately, and that is where all the trouble begins. That day, after dark energy is released, Diana makes Adam walk Cassie home. After a few minutes of awkwardness, Adam and Cassie cannot deny their intense and deep attraction to each other. They share a passionate kiss and the silver cord brings them together. But it is not until the fourth book that Adam and Cassie are finally allowed to be together. Cassie eventually becomes the official leader of the coven.

In regards to Adam and Cassie's relationship, Adam and Cassie are ultimate soulmates. They are bound together by a mysterious 'silver cord', also known as the silver cord of destiny or the silver cord of fate. This special cord links both Adam and Cassie from heart to heart, implying that the two are destined for each other for all of eternity and in any many, many lifetimes to come. It also means that regardless of time, space and distance, they will always be pulled towards each other no matter what. Adam and Cassie meet in Cape Cod at the beach and both of them see the silver cord binding them together. When Cassie moves to New Salem she discovers that Adam has a girlfriend, Diana. Diana has been a true friend to Cassie and the two have become almost sisters. Cassie cannot bring herself to tell Diana that she loves Adam. Adam cannot bear to hurt Diana.

After a midnight interlude at the beach, Cassie and Adam make a blood pact to never by word or look or deed hurt Diana and give in to their desires to be together. While making their pact, Adam and Cassie are spotted by Diana's cousin Faye. Faye uses her knowledge of Cassie and Adam's love to blackmail Cassie into doing what she wants. Cassie agrees as long as Diana does not find out, but soon she cannot take Faye's demands. In retaliation Faye tells Diana and the rest of the Circle about Cassie and Adam. Both Cassie and Adam beg Diana for forgiveness and to prove that they can be faithful to her and she agrees. Adam stays with Diana, but things have changed.

At the end of the trilogy, Diana gives Cassie her chalcedony rose, which has symbolized her love with Adam, and in essence giving her blessing for Adam and Cassie to be together since it is their destiny. Diana explains to Cassie that the only reason she told Cassie she continued with the charade was to prove to Cassie how strong she was. Adam and Cassie reunite and the trilogy is complete.

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