On the day that Christina becomes a U.S. citizen she receives a call from her younger sister and learns that their mother has had a heart attack. Reluctantly, she travels back to Scotland on a journey that forces her to confront everything she has tried to get away from—including her abusive dad who she learns may not be her father after all. What makes us who we are? Can we choose our own destinies? These questions are at the heart of Stem.