Ireland, 1924. Reverend Mother Aquinas is buying buttered eggs in the Cork city market at the very moment when the city engineer, James Doyle, is assassinated. Although no one saw the actual killing, a young reporter named Sam O'Mahoney is found standing close to the body, a pistol in his hand, and is arrested and charged. Following a desperate appeal from Sam's mother, convinced of her son's innocence, the Reverend Mother investigates - and in this turbulent, war-torn city, uncovers several other key suspects.