A deceased mathematical genius, his two very different daughters and a young and ambitious mathematician are the protagonists in this psychological cat-and-mouse game revolving around a mysterious calculation of ground breaking significance.

The young mathematician Hal Dobbs has taken upon himself the task of reading through all 103 of the compulsively written notebooks of his former teacher Robert who has just died. Robert, whose funeral is shortly to take place, was regarded as a mathematical genius until he became mentally deranged at the age of twenty-four. After the death of his wife, his younger daughter Catherine cared for him, relinquishing her mathematical studies in which she showed great promise, to save her father from a life in an institution. A life of seclusion in the family home in Chicago together with her ailing father has turned Catherine into a reserved, inscrutable young woman. Meanwhile her sister Claire carved out a successful career for herself on the New York Stock Exchange thus enabling her to support the family financially.

Robert’s last years, with the exception of nine months in which he recovered his mental balance, were marked by a manic urge to write. He filled notebook after notebook with compulsive scribblings and Hal, who regarded Robert as his spiritual father, is convinced that somewhere in the midst of this chaos, he will find something of great mathematical importance – something that Robert wrote down when for a few lucid moments his genius once again asserted itself. However, after three days spent scrutinizing the notebooks, he remains unsuccessful and Catherine is on the verge of losing patience with him. Although outwardly maintaining the notebooks to be worthless, she is nevertheless obsessed by the fear that Hal could misappropriate something of value. When she finds one of the notebooks in his coat pocket, she immediately calls the police. Hal’s explanation that he wanted to give her the notebook on her birthday as it contained a moving reference to her, convinces Catherine of her paranoia. When the police arrive Catherine is alone.

The following day Claire arrives for the funeral. Her energetic manner and her solicitous questioning of Catherine make it clear that she suspects her sister of inheriting not only her father’s brilliance but his mental instability as well and she
therefore plans to take Catherine to New York with her where she can keep an eye on her.
During the wake, Hal and Catherine are drawn closer together and Catherine, having overcome her initial dis trust of him, now appears to thrive on his obvious regard far her. The strain and tension of the preceding days disappear and both are now motivated by their mutual attraction.

The next morning Catherine’s low spirits have vanished completely and as Hal has shown himself to be sensitive and understanding, she entrusts him with the key to a secret drawer in the study. Shortly afterwards Claire reveals to her sister that she has sold the house to the university without Catherine’s knowledge. During the heated quarrel that ensues between them Hal bursts in, ecstatic over his discovery of a notebook containing ground breaking calculations concerning prime numbers.

But Catherine has a further revelation to make – one which will put the entangled
relationships of the three to yet another test.