Libby Day survived the brutal massacre of her family when she was just eight years old, testifying against her brother Ben, who was convicted for the murders. Now, 25 years later, she lives a lonely and troubled life, scrounging for money and disconnected from the world. When she is approached by members of the Kill Club, an amateur group obsessed with investigating notorious crimes, they offer her money to revisit the case and reconsider Ben's guilt. Desperate for cash, Libby reluctantly agrees and begins to uncover unsettling details that challenge her initial testimony and force her to confront dark memories she had long buried.

As Libby digs deeper into the events of that fateful night, she uncovers discrepancies and hidden secrets about her family's past. She revisits people from her old life, including her troubled mother and the friends her brother associated with. Each revelation gradually alters her understanding of what truly happened, leading her down a dangerous path filled with unexpected twists and moral complexities. As she pieces together the truth, Libby realizes that discovering what really happened might be more devastating than she ever imagined.