A year after his father's death, Oskar, a troubled young boy, discovers a mysterious key he believes was left for him by his father and embarks on a scavenger hunt to find the matching lock.

Mona Gray is a 20-year-old loner who, as a child, turned to math for salvation after her father became ill. As an adult, Mona now teaches the subject and must help her students through their own crises.