In 1846, Anthony Hope sails into London with the mysterious Sweeney Todd, a once-naive barber whose life and marriage was uprooted by a corrupt justice system. Todd confides in Nellie Lovett, the owner of a local meat pie shop, and the two become partners, as Todd swears revenge on those that have wronged him and decides to take up his old profession.

When his partner is killed, tough Irish detective Eddie Ryan vows to avenge the death, whatever the cost. As he begins unraveling clues, his behavior becomes so outrageous that he's obliged to turn in his badge, but the experience only emboldens him. Ryan eventually learns that his partner was caught up in a Puerto Rican gun-running scheme masterminded by a crook named Sweet Willie, who wants to foment revolutionary war.