In November 2000, the international press reported an amazing find: a mummy, which was claimed to be that of an ancient Persian princess, over 2,600 years old. She was encased in a carved stone coffin, inside a wooden sarcophagus and was wearing an exquisite golden crown and mask.

Her cloth-bound body was dressed with golden artefacts, with an inscription on her breastplate that read, "I am the daughter of the great King Xerxes, I am Rhodugune." All the internal organs had been taken out of her body, in the same way that the ancient Egyptians mummified their dead. It was the find of a lifetime, one of the most magnificent ancient treasures ever to be unearthed in the area.

When the curator from the Karachi National Museum, Dr Asma Ibrahim, began her investigations into the mummy, a different story began to emerge. Horizon follows the story as forensic experts all over the globe analyse the mummy and her magnificent trappings and discover that she is an elaborate fake with a terrible secret.

The mummy was found in a house in the desert region of Pakistan during a police raid, after a tip-off that it was to be illegally sold on the antiquities black market for $20m, and smuggled out of Pakistan. The Persian princess was immediately hailed as a major archaeological discovery. In fact, no Persian mummy had ever been found before, let alone a royal mummy. Mummification to preserve bodies had always been thought to be unique to the ancient Egyptians.

However, there were some strange puzzles about this beautiful princess. The inscriptions on the mummy's breastplate had some grammatical errors. And there were peculiarities in the way she had been mummified. Several detailed operations common to Egyptian mummifications had been omitted. So it began to look like the mummy was not the princess she was supposed to be; perhaps she was a more ordinary ancient mummy dressed up to be a Persian princess by forgers trying to increase her value.

As scientists investigated more closely, it became clear that this mummy had an even darker history. Computerised tomography (CT) scans and X-ray photographs of the body inside the mummy revealed that this was no ancient corpse but a woman who had died in the recent past, and that her neck was broken. An autopsy confirmed that this woman may indeed have been murdered to provide a body for the fakers to mummify - a body they intended to pass off as an ancient mummy for millions of dollars on the international art black market. And, finally there is evidence to suggest that they have done this not once but three times, raising the spectre of a mummy factory and the terrifying thought of yet more victims.