Julius Green, a Christie expert, found five full-length plays and five one-act dramas while scouring archives containing her papers.

Ten works by English crime novelist Agatha Christie, including five full-length plays and five one-act dramas, have been unearthed by a British theatre producer.

Julius Green, a Christie expert who has produced more than 250 plays and musicals, found five full-length plays and five one-act dramas written by the creator of the fictional Belgian detective, Hercule Poirot, while scouring the archives containing her papers.

Some are previously unknown and the others are long forgotten. The material lay in several archives, including those of Christie’s family and her theatrical producers, to which Mr. Green was given unprecedented access.

The plays will feature in Mr. Green’s book Curtain Up: Agatha Christie — A Life in Theatre, to be published next month ahead of her 125th birth anniversary. They include adaptations of Towards Zero, her 1944 novel, and The Stranger, a thriller about a woman who discovers her husband is a serial killer. The others are The Clutching Hand, showing the investigation of a series of murders by Craig Kennedy, a detective created by the American writer Arthur B. Reeve, and Someone at the Window, inspired by a short story of Christie’s called The Dead Harlequin, The Sunday Times reported.

Until now nothing has been known about Someone at the Window, apart from its title. Believed to date from 1934, it is “brimming with witty banter and social commentary about inter-war Britain,” Mr. Green said.

There is also a three-act domestic drama called The Lie, which is about infidelity, and was written during the failure of Christie’s marriage to her adulterous first husband Archie Christie.

Mr. Green found the script for Towards Zero in the archives of the Shubert Organisation, the oldest theatrical production company in America. The 1945 work is “entirely different” from Gerald Verner’s stage adaptation 11 years later.

He said there was “huge potential” to bring some of the “new” plays to audiences.