Jo Grayson is enjoying thoughts of a new life and remarriage when police arrive with surprising news that her husband Stephan - a research psychologist with a passionate interest in twins - has been killed in a hit and run car accident. That report presents an immediate riddle. As Jo seeks the solution to her problem, "The Gemini Hypothesis" reveals that - beneath a fragile veneer of respectable life - human character conceals dark secrets and sometimes masks pure darkness.