The episode begins with Rossi receiving a mysterious package that contains a personal item and a note from an anonymous sender, claiming to be his daughter. This news shocks Rossi, as he had no previous knowledge of having a child. Intrigued and confused, he decides to investigate the claim.

Rossi seeks the help of his colleagues on the Behavioral Analysis Unit (BAU) to uncover the truth. They analyze the package, the note, and the personal item with the hope of finding clues that will lead them to the sender. The team uses their profiling skills to narrow down the pool of potential suspects.

As the investigation progresses, Rossi begins reflecting on his past relationships and realizes that he had a brief affair many years ago. He starts to suspect his former lover could be the sender. To confirm his suspicions, Rossi reaches out to her and sets up a meeting.

During their meeting, Rossi confronts his former flame about the possibility of having a daughter and she confesses that it is true. She explains that she kept the child a secret because she didn't want to disrupt Rossi's life, but after seeing recent news about his involvement in a high-profile case, she felt it was time to reveal the truth.

In the end, Rossi learns that he does indeed have a daughter and the two of them slowly begin to build a relationship. This episode highlights the emotional journey of Rossi as he discovers an unexpected family connection and navigates the complexities of being a father.