The day before Agnes Cook is going to reveal her time machine to the world, her mother Claudia dies from an apparent suicide. Agnes is convinced that if Claudia hadn't gotten pregnant as a teenager, she would have had a better life and wouldn't have killed herself. Agnes' love for Claudia is so strong that she's willing to jeopardize her existence to save her mother. She uses the time machine to go back in time to the night her parents created her and stops them from having sex.

When Agnes returns to the present, she discovers that her plan didn't work. Later that same night, Claudia hooked up with a different boy, and had a daughter named Agnes. Claudia again dies from an apparent suicide. The second Agnes goes back in time and stops Claudia from having sex with the second boy, but still later that same night Claudia hooks up with a third boy which results in a third Agnes. Each voyage in time creates a new Agnes and brings Claudia closer to her true love. Soon, Agnes learns that there are some things you can never change.