From cut-throat to throat-cutter: Johnny Depp is the demon barber Sweeney Todd

In a film adaptation of the Stephen Sondheim musical, Sweeney Todd, as ever, Depp's metamorphosis into the the vicious barber who collected human parts for Mrs. Lovett's meat pies, is completely authentic.

With his pale face, sunken eyes, and shock of dark hair punctuated by a Mallen streak, Depp looks terrifyingly authentic as the 19th century mass murderer.

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Edward Scissorhands director Tim Burton has managed to enlist Depp to create a faithful film adaptation in which most of the action unfolds in song. Depp was a revelation, and surprised himself with his singing ability.

He said: "I knew I could stay in key to some degree. But I didn't know if I could sustain a note, or belt one out."

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Sweeney Todd spins a gruesome tale of vengeance in 19th-century London. Director Burton insisted on lashings of blood as his ghoulish barber slashed clients in the gory scenes.

But Depp admitted he soon tired of the sight of it.

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Depp told US magazine Entertainment Weekly: "I remember everyone except me being covered in plastic trash bags. There'd be a countdown: 'Three, two, one action!' And then blammo the great deluge.

"It tasted kind of like a Karo-syrupy sort of thing. It was oily and it was dangerous, slippery.

"You'd see these big English grips, tiptoeing through the swamp of blood."

Alongside Depp, the cast includes Burton's partner, Helena Bonham-Carter.

Bonham-Carter plays Mrs. Lovett, Todd's partner in crime. Desperate to be part of Todd's life and to exorcise his dead wife's ghost, she becomes his business associate, grinding victims into meat pies and selling them to an unsuspecting public. Alan Rickman, and comic actor Sacha Baron Cohen also star.

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In the film, Sweeney Todd is a man previously known as Benjamin Barker - who has returned from the penal colonies in Australia, where he has spent 15 years after being falsely accused of a crime.

When he speaks to Mrs. Lovett, maker of the worst pies in London, he learns that while he was away, his wife was raped by Judge Turpin, the man who sent him away. Distraught, she poisoned herself. The judge now has Sweeney's daughter under his thumb as his ward.

Sweeney Todd vows revenge, and Mrs. Lovett agrees to be his co-conspirator. Their plot brings about mass murder and amazing business for the pie shop.

The DreamWorks film is set for release in January 25.