Stars of stage and screen including Sir Patrick Stewart, Julie Walters and Miranda Hart are taking to the stage for a gala performance to celebrate the 60th anniversary of The Mousetrap.
The show, an Agatha Christie whodunit, was due to run for just six weeks when it opened in London's West End in 1952.
It has since become the world's longest-running stage production and is about to reach its 25,000th performance.
Hugh Bonneville and Tamsin Greig will also appear in tonight's one-off staged reading to mark the milestone.
Downton Abbey star Bonneville will play guesthouse owner Giles Ralston, with Greig playing his wife Mollie.
Iain Glen will play policeman Sergeant Trotter, with Hart appearing as guest Miss Casewell.
Walters is cast as Mrs Boyle while Stewart is to play Mr Paravicini.
It will be directed by Phyllida Lloyd, whose films include Mamma Mia! and The Iron Lady.
When the production opened at the Ambassadors Theatre in 1952, Lord Attenborough and his wife Sheila Sim took the lead roles.
It played there for 21 years, moving to St Martin's Theatre next door in 1973 without missing a performance.
Over the years, more than 400 actors and in excess of 200 understudies have worked on the play.