After being wrongfully imprisoned for fifteen years by the corrupt Judge Turpin, Benjamin Barker returns to London seeking vengeance. Under the pseudonym Sweeney Todd, he reopens his barbershop above Mrs. Lovett's pie shop, where she struggles to stay afloat due to the scarcity of quality meat. Barker's motive is not solely personal revenge on the judge who coveted his wife and daughter but also to avenge the injustices committed against the helpless people of London. As Todd, he becomes a skilled and diabolical barber, transforming his chair into a place of retribution for those he deems deserving of his razor-sharp justice.

Todd's dark quest is further fueled when he learns from Mrs. Lovett about the fates of his wife and daughter following his conviction. Their bond deepens as she becomes complicit in his mission to exact revenge. As Todd slices through the throats of his clientele, the two come up with a grisly solution to Lovett's failing business: incorporating the remains of Todd's victims into her meat pies. This unholy alliance leads to a macabre cycle of murder and profit, embedding them both deeper into the underbelly of London's grimy streets where morality is as scarce as Lovett's previous pie fillings.