In Canada, the sixty-year-old immigrant secretary Nawal Marwan passes away and the notary Jean Lebel, who had been her employer and friend for seventeen years, reads her will to her twin son and daughter Simon and Jeanne Marwan, who is a mathematician. Nawal requests to be buried naked with her face down and her tomb without a gravestone; further, she leaves three sealed envelopes addressed to the twins' father that they believed had died in the Middle East; to their unknown brother; and the last one to themselves to be opened only after the delivery of the other two. Then, they may put a gravestone on her tomb. Simon is reluctant to respect his mother last wishes, but Jeanne decides to find her biological father and brother. She travels to the Middle East to track down the past life of her mother and she discovers who she was before moving to Canada. She feels disturbed with the revelations and asks Simon to come to the Middle East to assist her in her journey. Simon discovers who his father and his brother are and concludes that one plus one may be equal to one.