In early March of 1362 Dom Pedro, King of Portugal, arrives in Oporto to make merry with its inhabitants on the last day of Carnaval. The townspeople are delighted with his arrival and celebrate the last day before Lent with music and dancing in the streets, drinking and feasting, and the lighting of bonfires. The king attends a great feast and dance at the bishop's palace then goes out to wander among the common folk. It is a joyous occasion for all. That is . . . almost all.

Shortly after dawn on Ash Wednesday the body of a beautiful naked woman is discovered. She was stabbed and her remains abandoned in a street. She is quickly identified as Berengaria, the young wife of Randolfo an elderly but quite wealthy inhabitant of the city.

Dom Pedro is quite disturbed by this crime which reminds him all too vividly of the great tragedy of his own life and is determined to discover the person responsible. However, it soon becomes clear that Berengaria's killer is likely to be found among the elite of the city, indeed among the guests at the feast Pedro himself attended. Discovering and punishing the criminal may have unwelcome consequences.