In 1834, a house fire at an elegant mansion in New Orleans, Louisiana, led to a shocking discovery. It was the dark and terrible days when the practice of slavery still shamed so-called civilised society – and behind this genteel Southern facade was a house of horror….

Born in 1787, in then Spanish-ruled New Orleans, Marie Delphine Macarty, known as Delphine, was a well-connected young woman from a respectable and wealthy family. She seems to have lived most of her early life in the normal, privileged fashion of New Orleans high society.

However, she was to become notorious as a woman who tormented, tortured and killed her unfortunate enslaved workers – and one of the most brutal serial killers ever – renowned in New Orleans lore as the infamous Savage Mistress.

But how much of this tale is fiction, how much fact..?

LaLaurie’s first husband was a well-connected Spanish royal officer, who died after just a few years of the marriage. Her second husband was a prominent banker, merchant and lawyer and the couple were married for around eight years until his death in 1816.

Then the wealthy, widowed Delphine became pregnant by a young French physician named Louis LaLaurie. The couple married after their child was born in 1826 and she moved into his home and took control of the large number of slaves there.

And some claim that it was at this point that Delphine began her descent into depravity – as a direct result of her marriage to Louis LaLaurie, who was apparently well known for his sadistic tendencies.

Over the next few years, her neighbours made a series of complaints to the authorities about her alleged mistreatment of her servants, but it seems these were not investigated. Bad treatment towards slaves was, shockingly, not uncommon at the time.

Wealthy slave owners were terrified by the slave revolts in Haiti between 1791-1804 and New Orleans in 1811, with the reports of attacks against whites. Many owners used increasing violence and oppression with the intent of quashing such behaviour. They believed that, without the threat of tremendous violence, their own slaves would rebel.

The forms of punishment were extreme. The 1811 revolt saw over 100 slaves beheaded, their heads put on poles stretching for 40 miles from the centre of New Orleans into the countryside.

This growing sense of panic probably explains why no investigators called to check on the reports of LaLaurie’s cruelty and why she never faced charges… until 1833, when a small slave girl fell off a roof and died, while trying to escape a beating from LaLaurie.

LaLaurie tried to cover up the incident, but police found the body hidden in a well and the authorities fined her and forced the sale of her other slaves. However, she foiled this plan by secretly having her relatives and friends buy the slaves. She then sneaked them back into the mansion, where she apparently continued to mistreat them – until one night in April 1834.

On that night, legend has it that a 70-year-old slave cook – chained to the stove by LaLaurie and slowly starving to death – started the fire. And when concerned locals rushed to help put out the fire, it was said they met with unimaginable horrors…

For, in attic of the mansion, it was claimed the would-be rescuers found heaps of human corpses, organs and limbs. Slaves pinned to tables or squashed in small cages, chained to roof beams in spiked iron collars. Living victims with their eyes gouged, fingernails torn out, ears hanging by shreds of skin, or their mouths sewn shut.

Others had their skin flayed, the wounds festering. Many accounts claim one woman’s skin had been peeled off in spirals to make her look like a caterpillar, another had bones broken and reset so she looked like a crab. One victim’s intestines were torn out and knotted around the waist. Many of these victims (some allege there were up to 100) were supposedly still alive – putrid and starving.

However, many believe the wild reports of the horrors LaLaurie is said to have inflicted have been greatly exaggerated, and to have grown in the telling over the years – although her behaviour was certainly monstrous. And yet others suspect that her doctor husband Louis was experimenting with Haitian voodoo potions to try to make his servants more docile, and that it was he who mutilated his enslaved workers in cruel, half-medical experiments.

Whatever the case, an outraged mob gathered in protest after learning about Delphine LaLaurie’s alleged torture chamber. She and her husband fled by boat and apparently escaped to Paris. Although charges were never filed against LaLaurie, her reputation in upper-class society was destroyed.

It is believed that she died and was buried in Paris in December 1842, though some claim her body was disinterred and moved to a cemetery in New Orleans in 1851. Other reports say that she actually faked her own death and returned secretly to Louisiana.

Many believe that Delphine LaLaurie was suffering from some form of mental illness. But other social historians claim that the really scary truth is that LaLaurie simply didn’t understand that what she did was wrong. Because – unthinkably ­– her behaviour was not out of the ordinary for slave owners in Louisiana, and that she was a product of her times.

So, while Delphine LaLaurie was a monster, she was one among many – and personified a dehumanising evil that could show its terrifying face in almost anyone…