This article is part of Yahoo's 'On This Day' series
It is the ultimate whodunnit.
That is because, for the most part, the only people who know the twist ending of The Mousetrap are those who have seen it.
For those yet to watch Agatha Christie’s famous play on the stage, the identity of the murderer - there is always a murderer when it comes to Christie - remains a mystery.
And you won’t get any spoilers here, either.
Plot aside, The Mousetrap is most famous for its longevity. And on this day 51 years ago, it became the world’s longest running play, a title it has never relinquished.
On 23 December 1970, Christie’s work took that accolade from the American play The Drunkard, which opened at the Theatre Mart in Los Angeles in 1933 and ran for 36 years.
At that point, The Mousetrap had chalked up an amazing 7,511 performances.
And after that, it just kept running. And running. And running.
It ran continuously in London’s West End from 25 November 1952 until 16 March 2020, when performances had to be halted because of the coronavirus pandemic.
But it still tops our list of the world's longest running plays...
The play has been running in London’s West End since 1952 and there have been more than 28,000 performances.
Christie famously said she did not expect it to run 14 months.
“It won’t run that long. Eight months perhaps. Yes, I think eight months,” she said.
Based on Victor Hugo’s novel of the same name, Les Mis is the longest running musical in the West End.
It has been running since 1985 and has notched up about 14,000 performances. It also had a 16-year run on Broadway in New York, comprising more than 6,600 shows.
The Phantom of the Opera
There have been more than 13,000 performances of Phantom in the West End since 1986, and a similar number on Broadway, where it opened two years later.
The Woman in Black
Susan Hill’s horror play has been running in London’s West End since 1989.
In that time it has had more than 12,000 performances.
It is the second longest running non-musical play in the West End after The Mousetrap.
MORE FROM THE 'ON THIS DAY' SERIES:
The revival of Blood Brothers ran in London’s West End from 1988 to 2012, taking in more than 10,000 shows.
It is the longest-running revival in West End history - it had a short initial run in 1983.
Andrew Lloyd Webber’s Cats closed on its 21st anniversary, having run from 1981 to 2002 in the West End, comprising almost 9,000 shows.
It held the record for longest-running West End musical for 17 years until it was overtaken by Les Misérables.
An 18-year run on Broadway between 1982 and 2000 saw more than 7,000 performances.
The Abba musical has been running for more than 8,000 performances in London since 1999.
It also had a 14-year run of more than 5,700 shows on Broadway between 2001 and 2015.
The Lion King
The stage version of The Lion King has racked up more than 8,000 performances since it opened in the West End in 1999.
This was two years after it opened on Broadway, where it also continues to run.
Watch: The Mousetrap reopens after COVID pandemic break