A man walks into a barbershop and notices a picture of Sweeney Todd on the wall. The barber begins to tell him Todd's story, which took place 100 years ago in the same premises.

In Victorian Britain, Mark, a sailor, tells Joanna of his love for her, although he knows that her father, a ship owner named Stephen Oakley, will forbid their engagement because Mark doesn't have enough money.

Oakley arrives and commands Mark to leave, before sending Joanna back home. Sweeney Todd, who has been hiding on the quayside, approaches Oakley, who thanks him for tipping him off about Mark's arrival

Todd receives a new apprentice, Tobias, and tells him not to speak to anyone about what goes on in his barbershop. His gives Tobias a penny to buy a pie from the shop next door run by Mrs Lovatt. Lovatt uses a secret passage to come over to Todd's shop, before complaining to him that he is squandering the money they have worked for.

Todd attracts a rich sailor into his shop. He puts him in a special chair that tips into a trap door at the pull of a lever, sending the sailor to his death in the cellar below.

Meanwhile, the crew of The Golden Hope, a ship owned by Oakley, reach the African outpost of trader Patterson, and get involved in a fight with the natives. The ship's Captain dies in the conflict, leaving Mark, who was one of the crew, to take over his station.

Todd threatens Oakley, demanding he repay the debts that are owed to him in respect of The Golden Hope. However, Todd suggests an alternative - the cancellation of all debts in return for Joanna's hand in marriage.

The Golden Hope returns with Mark as its Captain; he is now rich enough to marry Joanna. Todd is waiting for him at the quayside, and suggests that he needs a shave before meeting Joanna. Todd places him in his special chair and sends him down into the cellar.

Mrs Lovatt, who has been spying on Todd, takes Mark's body and hides it before Todd arrives to kill him. Todd questions her, but she manages to convince him that Mark escaped of his own accord through the secret passageway. Todd is unconcerned, for he has stolen Mark's money, leaving him still too poor to marry Joanna. When Todd leaves, Lovatt helps Mark to escape.

Todd's regular dealer in stolen goods comes to the shop, and threatens to tell all that he knows about how Todd receives his riches unless he is paid £7000. Todd attacks and kills him. Meanwhile, Mark hatches a plan to expose Todd, and disguises himself as a farmer to infiltrate the shop.

Mark arrives at Todd's premises and sends Tobias to Joanna for his protection. Tobias tells Joanna that Mark is there, and she disguises herself as a boy apprentice, so that she too can enter the shop and help Mark.

Todd sits Mark in the special chair, and sends him down the trapdoor. But Mark's friend is waiting downstairs and together they leave through the secret passage. Todd comes down to find them gone, and attacks Mrs Lovatt, who he suspects has aided their escape, knocking her unconscious.

Joanna arrives and seeks to convince Todd of her worthiness as an apprentice. He discovers that she is carrying a large amount of money, and knocks her unconscious in order to steal it. He sets fire to the shop in an attempt to burn the evidence of his actions.

Mark and his friends arrive, and Joanna's maid informs him that Joanna is in the burning building. Mark goes in to save her and struggles with Todd, who is knocked onto the special chair. Mark and Joanna escape, and a beam of wood falls onto the chair's lever, sending Todd to his death in the cellar below.

Back in the present, the barbershop customer asks what he can smell cooking, only to be told by the barber that it is the cooked meat shop next door. The man flees the shop in fright, and runs down Fleet Street into the distance.