Catherine, who sacrificed college to care for her mentally ill father (once a brilliant, much admired, mathematician), is left in a kind of limbo after his death. Socially awkward and shut in, she is gruff with Hal, a former student who shows up even before the funeral wanting to root through the countless notebooks her father kept in the years of his decline, hoping to find mathematical gold. On the heels of his arrival comes Claire, Catherine's cosmopolitan, blandly successful, and pushy sister, with plans to sell their father's house and take Catherine (whom she's convinced has inherited a touch of their father's illness) with her back to New York. Catherine does not want to leave, and things become more complicated as she and Hal tentatively begin to develop a relationship. She gives him a key to a drawer in her father's desk, where the "gold" waits in the form of a notebook filled with the most original and astonishing mathematical proof Hal has seen in years. Thrilled, he wants to take immediate steps to have the proof established in her father's name, until Catherine shocks both him and Claire by declaring that she is the author.

Claire doubts her claim and this exacerbates her doubts of Catherine's own sanity. Hal, who has professional ambitions of his own, isn't exactly disinterested and may not be trustworthy; his budding relationship with Catherine may also have complicated the issue!

A Pullitzer Prize and Tony Award winning play, Proof crackles with subtle wit while tackling large questions. The elusiveness of genius in general and the difficulty of a mathematical proof her become metaphors for the uncertainties of love,trust and personal integrity.