Colvin College is still reeling from the fire that destroyed the administration building last semester, and put a student, Margot Miller, in a coma, when Professor Moynihan announces he will be offering his famous “History of Lying” seminar to a select number of students. Cat Carlson is thrilled to be accepted into the course: Moynihan is a celebrity on campus and is releasing his very own lie-detecting technology, CUFF, later in the year. But the class—“The Liars' Club”— discovers Professor Moynihan has his own agenda.

The game is afoot! Cat begins her investigtion with her best friend and podcast co-host, Allie. They look over Allie’s super-helpful, super-pink suspect board, which ranks the other Liars Club members' alibis by how suspicious they are. They realize that Naia's alibi is really weak. Not only that, but Allie points out that they don’t know why the professor is so sure the fire was arson. Steeling herself, Cat decides to confront both Naia and Professor Moynihan about their secrets.

Moynihan puts everyone’s truth-telling abilities to the test, literally, with a pop quiz experiment that reveals the biggest fibbers in the class. Uncertain how to navigate the treacherous course, members of the class begin forming tentative alliances. But can anyone be trusted in the Liars’ Club?

The students show up to class only to discover that they have been invited to a cocktail party at the Professor’s house. Their invitations contain secrets— ones that they are not allowed to share with anyone else. Of course, the Party Twins and Alvaro alliance immediately breaks the rules. Once at the house, the Liars Club discovers that their task is to return that secret to its rightful owner, forever binding them together. When Bella and Benedict’s cheating is revealed, however, more secrets spill forth.

While Moynihan expresses his confidence in Cuff to a local journalist, Cat’s is badly shaken. She discovers Allie and Harper confiding in each other about the Liars’ Club case and feels betrayed by her only friend. Left vulnerable and even more alone, Cat becomes the prime suspect when a video of her actions the night of fire is emailed to every student on campus.

The Liars' Club gets a chance to use Cuff on each other, testing the truth of their alibis. Things go askew, however, when the device proves Erika’s honesty: she was outside the administration building at the time of the fire, and she saw someone who looked like Wilson running away. Adding to the upheaval is Margot Miller’s recovery from her coma. Suddenly, there’s someone else who might have information about everything leading up to the fire. The Liars' Club may have narrowed down their suspect list, but the mystery is far from being resolved.

Margot Miller is awake—but isn’t taking visitors. That doesn’t stop Harper, though. When she finds out that she’s not the only Liars' Club member who snuck into the hospital, she goes to talk to Cat to share what she knows. But when The Colvin Cauldron publishes a shocking story about Allie, Cat realizes she may not have all the facts.