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: the marriage hasn't brough peace between Catholics and Huguenots. Realising her weakening power over her sickly son, King Charles, Catherine persuades him of a plot against his life. Mad with fear, Charles 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...