More accurately a love triptych than triangle, The Femme Fatale Hypothesis is the story of one spring in 2015 when three people form intimate bonds forged in the fires of their respective tribulations. As Rose Geddes's lung cancer progresses toward its inexorable end and her husband's ability to care for her diminishes, their widowed neighbor, June Danhill, stumbles into the middle of their intersecting crises. June's only son, daughter-in-law, and two grandchildren have recently moved to the West Coast. She embraces the opportunity to distract herself from her loneliness by helping to care for the Geddeses. But it isn't long before June realizes that Rose wants more from her than she is willing to give. Love and loss, family secrets, visiting vultures, the Memorial Park boys, a long-forgotten keepsake, morphine versus fentanyl, and the sexual cannibalism of the false garden mantid all fuel this psychological thriller that tests the thin line between mercy and murder.