Catherine is a twenty-five-year-old woman who recently dropped out of Northwestern University to become the sole caretaker for her mentally ill father. She lives in their rundown Chicago home, spending her days in a state of exhaustion and depression. Having inherited her father's mathematical aptitude, she worries constantly about her own sanity and fears losing her mind. She acts guarded and sharp-tongued, fiercely protecting her independence while pushing away those trying to help.

Robert is a celebrated academic who made groundbreaking contributions to the field of mathematics in his early twenties. He spent his later years suffering from a severe, debilitating mental illness that produced graphomania and delusions. He appears in the play through Catherine's memories, imaginations, and flashbacks to his lucid periods. He is a proud man who deeply fears losing his intellectual capacity.

Hal is a twenty-eight-year-old mathematician and former doctoral student of Robert's. He spends his days combing through the notebooks left behind by his late mentor, searching for a final mathematical breakthrough. He plays drums in an all-mathematician rock band. He recognizes his own work is unoriginal and feels desperate to associate himself with greatness.

Claire is Catherine's twenty-nine-year-old sister who lives and works in New York City. She funded her family's Chicago household from afar but largely avoided the day-to-day emotional toll of their father's care. She prefers a practical lifestyle away from her family's Chicago home. She is highly organized and approaches family crises with logistical solutions like real estate sales.

Mitch is Claire's long-time boyfriend who lives in New York. He recently became engaged to Claire, representing the stable and conventional life she has built far away from her family's Chicago home.