Alexander the Great remains one of the greatest empire builders in history. In 323BC, having conquered virtually the entire known world, he died in circumstances that have never been resolved. Was it a simple fever or was his death the result of more sinister causes?

This compelling documentary, with the expert help of one of the top detectives at Scotland Yard, Commander John Grieve, attempts to find out exactly what happened to the Macedonian king.

Alexander was a legend in his own lifetime. The seeds of his greatness were sown while he was still a youth. Tutored by the philosopher Aristotle, he became king of Macedonia at the age of twenty after his father, King Philip, was assassinated. He quickly displayed a genius for military strategy, brave and daring leadership and charismatic PR skills, attributes which saw him conquer Persia, and create an Empire stretching from Egypt to Afghanistan. "He built an empire on the cult of his personality", comments the narrator. Following a banquet in Babylon in 323BC, the King fell ill and after twelve days of fever he died.

"Macedonian kings do not just lay down and die in their sleep", says Robert Arnott, an expert in ancient medicine. So was his death caused by something other than disease?

Using thirty years of experience as a police detective, Commander John Grieve seeks to get to the bottom of Alexander's untimely death. However, with no body and 2,300-year-old sources, Grieve's task is not going to be easy. After pinpointing Alexander's death to 11th June 323BC, Grieve examines the wealth of historical information on Alexander's last days. There are two schools of thought, one that Alexander died of a fever, the other that the king was poisoned. Was his death of natural causes? Grieve knows Alexander was a heavy drinker and had also accumulated numerous war wounds. Could a high fever have overcome the physically weakened Alexander?

With the help of Dr John Marr, an expert on tropical diseases, Grieve tries to match a disease to Alexander's symptoms and in the process Marr brings a new clue to Grieve's attention. Not long before his fever, Alexander and his troops noticed birds falling out of the sky. Marr compared this to a similar incident in New York City in 1999, when birds were also reported falling dead from the sky. It wasn't long before there were human casualties from the disease, a virus called West Nile Fever. Could this have been the cause of Alexander's death? Grieve is intrigued by this possibility, but not convinced. "You have to keep an open mind and have a look at other theories," says Grieve. "Not least that of poison".

There is a wealth of historical information suggesting Alexander had enemies and that his army was approaching mutiny. As well as forcing his fatigued men to invade country after country, Alexander was promoting Persians to high positions in the army. "This didn't go down at all well", comments Oxford historian Robin Lane Fox. "A soldier had to sit next to someone who, only two years previously, they were trying to slaughter".

Alexander also had enemies within his own inner circle. He had sacked Antipater, the Governor of Macedonia, who, due to Alexander's reputation for violence and cruelty, then feared for his life. "The simple desire to survive would have been motive enough to kill [Alexander]", offers Professor Barry S Strauss. It is written that Antipater's son, Cassander, travelled to Babylon with poison supplied by Aristotle, whose nephew was executed by Alexander. With Dr Leo Schep of New Zealand's National Poisons Centre, Grieve pieces together the sequence of events and searches for the identity of the poison that might have been used. Was he poisoned at a drunken banquet, while co-conspirators distracted his attention? Schep thinks it is probable that he was poisoned several times during his fever to finally kill him off.

However, just as Grieve closes in on the culprit, an unexpected twist leads him to uncover a fascinating new explanation that could finally solve Alexander The Great's Mysterious Death.