Grace is the young supervisor of Short Term 12, a group home for troubled teenagers. She lives with her long-term boyfriend and coworker, Mason, but finds it difficult to open up to him emotionally. At the beginning of the film, Grace has an appointment with the doctor, who is going to give her unexpected news. She is not very happy with the news and is afraid to tell Mason, who starts to feel a little bit uneasy about Grace.
At the facility, Grace and Mason focus their efforts on Marcus, a Short Term 12 resident who is about to turn 18 and is struggling with the idea of leaving the facility. Mason is great at telling funny stories and cheering the kids in creative ways. His own experience as a foster child in a Mexican family has helped him sympathize perfectly with the residents of the group home.
Grace will have a great connection with Jayden, a recent arrival at the group home who has a story of self-harm. Jayden distances herself with the other teenagers as she does not intend to stay at the facility for long. Other teenagers at the group home are Luis, Sammy, Kendra…, a bunch of kids whose real family are the adults at the group home who listen to their problems, play with them and try to make their lives a little bit more bearable. Apart from Grace and Mason, Jack, the therapist, and Jessica, another social worker, share the responsibility of nurturing the teenagers’ broken lives. Working with the team is Nate, a young man out of college who is starting his counselling career at Short Term 12
In the group home the adults will try to create a safe environment for the kids, helping them to come to terms with their troubled lives and the reactions that their emotional injuries bring them. Why is Marcus afraid of leaving the house? Why is Jayden so silent about her life and her family? Why does Grace not tell Mason about her health?
In the facility, everyone will learn to deal with the burdens of the past, the surprises of the present and the hopes for the future.