The Secret follows the story of a family of three who move to Williamstown in hopes of starting a new life. The husband, Bill, is a professor at the local college, while his wife, Samantha, is a struggling artist. Their daughter, Sam, is a rebellious teenager who resents her parents for uprooting her from her life in Boston.
After a heated argument with her mother, Sam storms out of their house and takes the family car for a joyride. She loses control of the car and crashes into a tree, leaving both her and her mother critically injured. While in a coma, Sam's spirit is visited by her mother's ghost, who tells her that she needs to wake up and live for the both of them.
When Sam wakes up, she discovers that her mother has died from her injuries. However, she soon realizes that her mother's spirit has entered her body, causing her to act and speak like her mother. As the days go by, Sam struggles to adjust to her new life as her mother, while her husband and daughter struggle to come to terms with their loss.
Throughout the movie, the family learns the power of forgiveness and the importance of cherishing the time they have together. In the end, Sam's mother's spirit leaves her body and moves on, leaving the family to pick up the pieces and move forward with their lives.