In the West End of 1950s London, plans for a movie version of a smash-hit play come to an abrupt halt after a pivotal member of the crew is murdered.
In the West End of 1950s London, plans for a movie version of a smash-hit play come to an abrupt halt after a pivotal member of the crew is murdered. When world-weary Inspector Stoppard (Sam Rockwell) and eager rookie Constable Stalker (Saoirse Ronan) take on the case, the two find themselves thrown into a puzzling whodunit within the glamorously sordid theater underground, investigating the mysterious homicide at their own peril.
London's West End, 1953. As The Mousetrap, Agatha Christie's latest murder mystery play, celebrates its 100th performance, preparations are in progress for a film adaptation. Instead, a horrible backstage murder brings the ambitious plans to an unexpected standstill. Now, everyone involved is a suspect. And as seasoned Scotland Yard inspector Detective Sergeant Trotter and his enthusiastic assistant Constable Stalker sift through a long list of potential murderers, the question arises. Can the mismatched duo crack the knotty case before the shadowy killer strikes again?—Nick Riganas
London, 1953. Leo Kopernick has been murdered. He had just been hired to direct a film adaptation of the enormously successful Agatha Christie play The Mousetrap. Investigating the murder are jaded veteran detective Inspector Stoppard and his inexperienced but incredibly eager and resourceful assistant Constable Stalker.—grantss
In 1953 London, Agatha Christie's play The Mousetrap celebrates its 100th performance, and sleazy American director Leo Köpernick has been hired by producer John Woolf to allow him to direct the film adaptation. After Köpernick's drunken behaviour towards the female lead Sheila Sim leads to a fistfight with her husband and co-star Richard Attenborough, Köpernick is killed backstage by an unseen assailant.
Inspector Stoppard investigates the murder, shadowed by the inexperienced Constable Stalker. Everyone at the theatre is declared a suspect and a potential victim, including the play's producer Petula Spencer and Woolf's wife Edana Romney. Stoppard attempts to close the theatre until the murder is solved, but the Metropolitan Police Commissioner, Harold Scott, intervenes, assigning Stalker to assist in the investigation.
Stoppard and Stalker search Köpernick's room at the Savoy Hotel, finding his address book of women's details. The hotel manager recalls Köpernick's violent argument with screenwriter Mervyn Cocker-Norris, who admits to arguing with Köpernick over the director's vision for an action-packed ending for The Mousetrap film. Mervyn, who lives with his hot-headed "nephew" Gio, remembers a "plain woman" arriving at the hotel with Köpernick's son.
Stoppard and Stalker question Woolf, who was blackmailed by Köpernick after he discovered Woolf's affair with his assistant, Ann. Dennis, an usher at the theatre, offers an unhelpful description of a suspicious figure; Attenborough and Sim are questioned as well. Spencer explains that she optioned The Mousetrap's film rights to Woolf, but he would be contractually unable to produce the adaptation until the show had closed.
At a pub, Stoppard bonds with Stalker and reveals that his unfaithful wife left him after having a child with another man. Driving a drunken Stoppard home, Stalker finds news articles and a picture of his ex-wife, fitting Mervyn's description of a "homely woman with glasses". Combined with Dennis' description, this leads Stalker to suspect Stoppard may be the killer, and she searches for his ex-wife in Köpernick's address book.
Stoppard and Stalker attend a performance of The Mousetrap, during which Mervyn, Woolf, Dennis, Gio and Stoppard leave the auditorium; Stalker soon follows after watching Stoppard retrieve his gloves. In the foyer, Mervyn is strangled to death by a gloved figure. Stalker spots Stoppard kneeling over the body and gives chase, knocking him unconscious with a snow shovel.
Stoppard awakens in a cell, and Stalker and Scott accuse him of carrying out the murders. Stalker has summoned Joyce, the mother of Köpernick's son, but she is not Stoppard's ex-wife, exonerating him. Stalker escorts Joyce and her son home, and Joyce mentions overhearing a man with a "village idiot" accent. Reading through Mervyn's research on The Mousetrap, Stoppard realises the identity of the killer and races to the suspect's apartment, where Stalker has already burst inside and found the necessary evidence: the killer is Dennis.
Attenborough, Sim, Woolf, Ann, Spencer and her elderly mother arrive at the home of Agatha Christie in Wallingford, Berkshire, having received invitations to dinner. The butler Fellowes is perplexed by their arrival, but Christie's husband, Max Mallowan, allows them inside. The group are held at gunpoint by Dennis, whom Spencer's mother recognises as Dennis Corrigan, an abused child whose brother's death inspired the plot of The Mousetrap. Dennis explains that he killed Köpernick and Mervyn in an attempt to stop the play and its adaptation, disgusted by the exploitation of his brother's tragedy for entertainment.
Having forged the invitations to lure everyone together, Dennis has captured Edana, mistaking her for Christie. Christie enters with tea, including a poisoned cup for Dennis which Fellowes inadvertently drinks instead. An armed Stoppard arrives and a shootout ensues; Sim distracts Dennis with a molotov cocktail, and Stalker nearly takes a bullet to save Stoppard, matching Köpernick's story pitch, before Agatha dispatches Dennis with a shovel. It is revealed that the bullet did, in fact, hit Stoppard. Some time later, Stalker passes her sergeant's exams and a recovering Stoppard receives the King's Police and Fire Services Medal, and they attend another performance of The Mousetrap together.
