In 1865, a corpse was discovered the day after Saint Patrick's Day in the Irish district of Griffintown, Montreal. Silas Robinson leads the investigation, assisted by his new collaborator, Miss Dupuis. At first glance, the inquiry focuses on what appears to be a simple brawl among Irishmen that took a fatal turn. However, the mystery deepens when Robinson is forced to explore other leads, this time with political overtones.