It is the greatest and most enduring mystery of the 20th Century - just what on earth happened to Lucky Lord Lucan?
Forty years ago this week, the Seventh Earl of Lucan mistakenly murdered his wife's nanny; he has never been seen or heard of since.
In the past four decades, there have been any number of theories as to what might have happened to this raffish, good-looking gambler. Did he escape to South Africa, to South America, or even to Alaska? Or did he take his own life after realising that his final throw of the dice had - yet again - ended in abject failure.
It is a fascinating tale - and yet very few people under the age of 40 know anything about it. Nobody outside Britain has ever heard of Lord Lucan.
I have told this story many times over. I've even written Lord Lucan's (made-up) memoirs - Lord Lucan, My Story. They are my own take on what might have happened to the missing Earl.
What I do know is that once people start to hear the details, they cannot fail but to be caught by the whole drama of the Lord Lucan scandal.
Of course this mystery stems from a tragedy - a terribly tragedy. Lord Lucan's nanny was bludgeoned to death with a piece of lead piping. Even today, her family still mourn her. The murder still casts a terrible shadow over Lucan's wife and his three children.
But what it is that mesmerises us now is not so much the murder, but the thought of how a handsome Earl could just disappear off the face of the earth. The story is so extraordinary it has about it all the fairytale qualities of a modern-day Rip Van Winkle.
So - in that spirit, here are 10 things you never knew about the man who styled himself as "Lucky Lord Lucan" - but who was in fact one of the unluckiest men in Christendom.
1. Lord Lucan was a professional gambler - though unlike most professionals, all he ever did was lose money. He managed to squander almost the entire Lucan fortune - about £7million today - at the casinos, particularly the Clermont Club in Mayfair, which was run by his friend John Aspinall.
And for a long time, it was believed that Lord Johnny Lucan was just not a very good gambler.
It was only when John Aspinall died of cancer in 2000 that it became clear that Aspinall was an out-and-out crook. As detailed in Douglas Thompson's definitive book The Hustlers, Aspinall was in league with the London mobsters. Aspinall provided the rich clientele for the casinos while the mobsters provided the card-sharps.
Aspinall's entire multi-million pound fortune - which bought and catered for the two wild-life parks at Howletts and Port Lympne - was earned by cheating.
One of Aspinall's favourite tricks was to fleece his friends at cards and then at the end of the evening, say, "Tell you what - double or quits on the cut of the cards."
This showed his friends what a good sport he was. Unfortunately for them, Aspinall always used a special deck of cards, a stripper pack, and would invariably cut the ace.
As Aspers once remarked, "It's very easy to steal from your own friends."
Having cheated Lucan out of his family fortune, Aspinall then kept him on at the Clermont Club as a house-player. Lucan was allowed to keep a small percentage of his winnings but, much more importantly, he added colour and status to the Clermont Club.
2. Lucan was fresh out of options by the time he'd hatched his insane plan to kill his estranged wife Veronica. Veronica was living in the family home in Belgravia with the three children, while the Earl was living in a nearby flat. He was up to his eyeballs in debt who spent his days wallowing in the interminable boredom of the Clermont Club.
Lucan would arrive at the club at lunch-time and then, every single day, without exception, he would have the same meal: smoked salmon and lamb cutlets. He'd play some backgammon or bridge, and would then return to the Clermont in the evening for the main session which usually went on till past 2am.
He was in a rut the size of the Grand Canyon. Murdering his wife must have seemed like an easy way out from the hell that he had created for himself.
3. Although we can't be sure what happened on the night of November 7, 1974, all the indications are that Lord Lucan had been planning to murder Veronica for some time. A few weeks earlier he'd borrowed a Ford Corsair from his friend Michael Stoop. It seems that he was going to use the Corsair to transport Veronica's body to the coast where he planned to dump her in the Channel. He was then going to claim that she'd done a runner - and that, he hoped, would be the end of his financial woes and would leave him free to bring up his son and two daughters.
On the night of the murder, Lucan had also set up an alibi, arranging to meet some friends for dinner. The most likely scenario is that he intended to murder Veronica at around 8.30pm. He'd then put the body into a US Air Mailbag and hide it in the boot of the Ford Corsair before having a quick dinner with his friends. After supper, he'd for the coast, dumping the body at sea, and then race back to London in time for breakfast.
4. When Lucan came up with this hellish plan to kill his wife, he must have thought that there could only ever be two outcomes - either Veronica would end up dead, or she'd still be alive.
What he could never have conceived of was that his wife's new nanny, Sandra Rivett, would change her night off. Instead of going out for the evening, Sandra decided to spend the night in with the family. By a complete freak coincidence, she also bore a very close resemblance to Veronica. They were both petite women and had similar shoulder-length hair.
The family had been watching TV upstairs when at about 8.30pm, Sandra went to the basement to make some tea.
Waiting for her in the kitchen was - as far as we can tell - Lord Lucan. The room was quite dark as he had unscrewed the bulb from its socket. In the darkness, Sandra must have looked very similar to Veronica.
Lucan attacked her with an 18-inch piece of lead piping, hitting her six or seven times on the head. He had put some white-tape around the end of the pipe so that he wouldn't lose his grip.
One can only imagine Lucan's horror when he realise that he'd killed the wrong woman. He was stuffing Sandra's body into the mailbag when he heard Veronica calling out. They had a fight on the stairs. He managed to hit her over the head with the lead piping, but she saved herself by kicking him in the groin.
5. Although Lucan had just tried to kill Veronica, they still had a chat on the stairs. One can only imagine how utterly surreal this conversation must have been - Veronica still dazed from the head injuries that Lucan had inflicted on her, while Lucan himself was spattered with Sandra's blood.
By all accounts, the conversation was quite calm. There was no shouting.
But even though it was only a few minutes after the murder, you can see that Lucan was already concocting an alibi for himself. He told Veronica that he'd been walking past the house when he saw Sandra being attacked by an intruder in the basement. He went in to help - only for the intruder to disappear into the night.
Some of Lucan's supporters have gone along with this theory. But as we shall soon see, Lucan was up to his aristocratic neck in the murder.
The conversation on the stairs lasted for a few minutes before Lucan went upstairs to wash the blood off his hands.
Veronica took her chance and fled the house. She ran down the street, bursting into the nearby Plumber's Arms. Covered in blood, she screamed for help and then collapsed on the floor.
One final poignant scene in the house before Lord Lucan left his home for the last time. By now, with Veronica out of the house, he must have known that the game was up. He knew that he probably had about 10 minutes to get away before the house was alive with police.
He was just leaving when his elder daughter Frances came out of her bedroom. "What's happening daddy?" she said.
"Nothing," replied Lucan. "Go back to bed."
And that, as far as we know, was the last time Lucan would ever see his children.
6. As soon as he'd left the murder scene, Lucan drove south to Uckfield in Sussex, where he stopped in to see a friend, Susan Maxwell-Scott.
By now, Lucan's story about the murder was beginning to crystallise. He repeated his claim that he'd just been walking past the house when he'd seen this mystery intruder attacking Sandra.
Susan - who was a lawyer - naturally suggested that he should give himself up to the police. But that was because she believed his repeated pleas of innocence.
Lucan had an hour or so to himself when he wrote a few letters. In one of these, he said he was going to "lie doggo" for a while until things had calmed down.
Susan offered him a bed for the night, but he insisted that he had to get going. She was the last person ever to admit to seeing Lord Lucan alive.
A few days later, Lucan's getaway car was found abandoned in the seaside town of Newhaven in Kent; the car was covered in his finger-prints as well as smears of Sandra's blood.
Lord Lucan has never been seen or heard of since.
7. Over the last 40 years, a number of Lord Lucan's supporters have come out to defend the Earl. They've said he was a gentleman; that he fled the country because he knew he'd never get a fair trial; and that, above all else, until he'd been proved guilty, Lord Lucan was an innocent man.
Both friends and family have gone along with this fanciful notion that he just happened to be in the wrong place at the wrong time. Some of his friends - and I've met them - have talked about how kind and gentle he was. They say that Johnny would have been physically incapable of murdering his wife.
The truth though - how ever unpalatable - is that Lucan had planned the murder from start to finish. It is just about possible that he hired a hitman to kill his estranged wife, but more than likely he did the job himself. And botched it himself.
There are several reasons why we know for a certainty that Lucan was involved with the murder. This evidence was certainly good enough to convince the jury at Sandra Rivett's inquest that she had been "murdered - by Lord Lucan".
First of all, of course, there is the sheer weight of circumstantial evidence - the Ford Corsair that he'd borrowed a few weeks earlier from Michael Stoop, as well as the supper alibi that he had painstakingly constructed for himself.
But there was also one piece of rock-solid evidence - a smoking gun which would inextricably link Lucan to the murder.
There was in fact not one murder weapon, but two. For some reason, perhaps as a back-up, Lucan had prepared a second piece of lead-piping. This was almost identical to the main murder weapon. It was about 18 inches long and it also had some white tape round the end.
The primary murder weapon, badly bent out of shape, was left in the house at Belgravia.
And as for the back-up weapon, that second piece of lead-piping...
The police found it in the boot of Lucan's getaway car after it had been dumped in Newhaven.
It seems that in his panic to get away, Lucan had forgotten to remove the back-up weapon from the boot of the car.
And with this one piece of evidence, the whole edifice of Lucan's concocted story is revealed as nothing but a tissue of lies. There is no getting away from it. If Lucan really was innocent, then how on earth did this second piece of lead piping end up in the boot of his getaway car?
It is just about possible that Lucan might have hired a hit-man, but it's far more probable that he murdered Sandra himself.
8. Over the last 40 years, every one of Lucan's friends has been approached by journalists to find out what they think happened to the missing Earl.
They have all said pretty much the same thing. They think he killed himself.
There are any number of reasons why they've thought he killed himself. They've said he killed himself because he couldn't take the shame of killing Sandra Rivett; that he couldn't take the guilt; that he couldn't bear the dishonour that he had brought to the Lucan family name; that he hated being a fugitive; that he couldn't bear to live outside the UK.
Any number of reasons why he killed himself - but they are all agreed on one thing. He killed himself. Definitely killed himself.
And so the case is neatly closed.
But what an astonishing uniformity of opinion. All of them saying the same thing: he's dead!
When as it is, the facts tend to point in completely the opposite direction.
That far from killing himself, he got away - and may, even now, be eking out his life in some foreign clime. He will be 80 on December 18.
First of all: his state of mind. Lucan was a gambler. Gamblers see things through to the last turn of the card. They don't tend to give up just because they don't like the look of a hand.
Secondly: where's the body? If you want to kill yourself, then you kill yourself. It's very rare that you kill yourself and then also manage to do away with your own body.
And lastly: One of the fascinations of the Lucan scandal is that any outlandish theory as to his whereabouts is just as viable as the next. You can think what you like about Lucan. Anything's possible! Some people have even come up with the risible claim that Lucan and Sandra were lovers.
But over the years, a few little dribs and drabs of evidence have filtered out. A taxi-driver saying that soon after the murder, he'd taken Lucan to a private airport; secretaries saying they'd arranged flights for Lucan's children to go out to Africa; his wrist-watch turning up at a pawn-brokers in South Africa.
It's not much - but together all this evidence certainly indicates that Lucan got away.
And the evidence for him committing suicide? Nothing but well meant supposition.
9. The key to Lord Lucan's getaway was, almost certainly, John Aspinall.
John Aspinall had not only the means and the motive to get Lucan out of the country, but he also had the opportunity.
Aspinall was a multi-millionaire whose mansion-house just happened to be quite close to Newhaven, where Lucan dumped the car.
He had many, many millions of pounds at his disposal - and no shortage of incoming money either, as there were always plenty more millionaire blue-bloods who were only too happy to be relieved of their fortunes by Aspinall's card-sharps at the Clermont.
Aspinall also had the sort of underworld contacts who could have spirited Lucan out of the country. He was already in cahoots with the London mobs: they were supplying him with all the card-sharps for his casinos. Getting Lucan out of the country was not going to be too much of a problem.
But - crucially - Aspinall had the motive. He was an unscrupulous shyster, but he did tend to stick by his friends - especially when they were on their uppers. It was he who had personally set about bankrupting Lucan, and it was this that may have tipped Lucan over the edge.
It's more than likely that Aspinall would have stood by Lucan in his time of need.
Apart from anything else, Aspinall was an out-and-out mischief-maker. He would have revelled in helping out Britain's most wanted man; would have loved thumbing his nose at the police and the establishment.
Once Lucan had got away, Aspinall had more than enough money to establish Lucan with property, wealth and a new identity.
10. It is difficult to under-estimate the devastating effect that Sandra Rivett's murder has had on not just her family, but also the Lucans.
Lucan's two daughters and his son and heir George face these constant reminders that their father was one of Britain's most notorious killers. As for his poor estranged wife Veronica - who is still very much alive - she is now all but defined by this horrific murder. For a long time she was estranged from all three of her children; she still calls herself the Countess of Lucan.
But this is a story which has gone way beyond these two families. It is now a legend which has become a part of Britain's national identity.
It is strange seeing how the Earl has so comprehensively wrecked the Lucan family name. For Lucan wasn't just the Earl of Lucan - he was the seventh in a long line of Earls. This lineage included the Third Earl of Lucan who presided over another catastrophe, the Charge of the Light Brigade.
And as it is... The name "Lord Lucan" has become such a standing joke that Lucan's son won't even touch the title, preferring instead just to call himself plain "George Bingham".
As Lucan eked out his life in whatever country Aspinall sent him to, he must have had many regrets: botching the murder in the first place; never seeing his children again; never seeing London again, or any of his friends. But it must also have been a cause of very great regret that this once proud name, "Lord Lucan", had now entered the English language as a byword for the ridiculous and the simply unbelievable.