The ageing Catherine de’ Medici has arranged the marriage of her beautiful Catholic daughter Margot to the uncouth Huguenot King Henry of Navarre. Margot, still desperately in love with Henry de Guise, refuses to utter her vows. But even Catherine is unable to anticipate the carnage that this unholy union is to bring about. In the midst of an August heatwave, tensions run high between the Catholic Parisians and the Huguenot wedding guests; Margot’s marriage to Henry has not resulted in the peace that King Charles longed for. Realising her weakening power over her sickly son, Catherine sets about persuading Charles of a Huguenot plot against his life. Overcome by fear, he agrees to a massacre that will rid France of its 'pestilential Huguenots for ever'. And so the carnival of butchery begins, marking years of terror and upheaval that will end in the demise of kings, and finally expose Catherine’s lifetime of depraved scheming.