All mysteries are morality plays, in which evil does not usually go unpunished. Mrs. Stanning killed a child, and though she served time in prison, “prison wasn’t bad enough for her,” as Trotter says. Although he is insane, he echoes his creator’s sentiments. Agatha Christie believed that capital punishment was just, that only a life can pay for a life, unless the murderer is not morally responsible, as Trotter clearly is not. Therefore he will be placed in an insane asylum. She also recognized that misfortune can befall those who are technically innocent of wrongdoing, for, as in a Shakespearean tragedy, once evil is unleashed, it cannot be controlled—thus the need for justice.

One sees in this play, too, one of the worst effects of crime: its creation of suspicion. The Ralstons love each other enough to brave a blizzard to go to London for anniversary presents, and they are working together to make their guest house succeed. Yet by the second act each suspects the other of infidelity, even of murder, and none of the guests trusts either fellow guests or the hosts.

Though the primary cause of this unease is the murder, social change also plays a role. Trotter points out that in the postwar world “there aren’t any backgrounds nowadays and young people settle their own affairs.” Mollie knew Giles only three weeks before she married him. Although the traditional mystery posits a well-ordered world in which crime is a temporary aberration, Christie suggests that in the modern era this assumption may be losing its validity.

In At Bertram’s Hotel (1965), Christie accepts the need for change, yet that novel is suffused with a deep nostalgia for a more elegant age. Similarly, Mrs. Boyle comments on the lack of amenities at Monkswell Manor, which as been converted to a guest house because the Ralstons cannot afford to maintain it any other way. Even with paying visitors they have trouble heating the place. Giles must be his own sign painter, Mollie her own cook, and her culinary skills seem largely confined to opening tins. Mysteries partake of the novel of manners, and The Mousetrap reveals an England of ration books and cold radiators, where the worm is in the oak and dry rot waits to claim stately homes. The portrait is not exaggerated; between 1945 and 1975, almost twenty stately homes disappeared in England each year, for a total of 595, and another 132 survived only because of the National Trust. Christie’s play evokes the England of John Piper’s pictures, Evelyn Waugh’s lament for a bygone age in Brideshead Revisited (1945), and the acceleration of the process that D.H. Lawrence notes in Lady Chatterley’s Lover (1928):The Georgian halls are going. Fritchley, a perfect old Georgian mansion was even now, as Connie passed in the car, being demolished. It was in perfect repair; till the war the Wetherleys always lived in style there. But now it was too big, too expensive, and the country was becoming too uncongenial.

The Mousetrap begins with the murder of a mysterious woman in London. The action takes place in a guest house thirty miles from London where a house full of suspects have gathered and where a second murder is about to be committed.

Appearances and Reality
At the heart of any mystery lies the question of what is real and what is not. This is particularly true of The Mousetrap, which relies on disguise to confuse the audience. The detective in the mystery genre is suppose to be the outsider, the member of the cast with whom the audience can most closely identify. But in this play, the appearance of the detective does not fulfill the audience's expectations, since the reality is that the detective is the murderer. Christie is playing with a genre which the audience thinks is predictable in its basic form, forcing them to employ analytical skills beyond the accustomed.

Death
Death provides both the opening of this play and the transition between acts. And yet, in one sense, death is almost the least important aspect of the play; solving the murder is the crucial element. Christie's first victim is unknown to the audience and the second is a complaining obnoxious woman whom the audience gladly sacrifices in the struggle to unearth a murderer. Thus, death becomes almost abstract, a necessary action to advance the plot but not an action which causes the audience any grief. The result is that death, rather than assuming a central position of importance in the play, becomes only a necessary contrivance which the author employs to entertain. However, in a second way, death has a separate importance. The motivation for the deaths that occurs during the play is the death of a small boy years earlier. It is this death that leads to the others, and since both victims are in some way responsible for the death of the child, once again the audience is able to absolve itself of any caring for the two female victims. And so, Christie provides a complexity to the theme of death that requires her audience to look beyond the obvious.

Justice and Injustice
This play can also be described as a search for justice. The two murder victims are responsible for the death of a young child and the abuse of his siblings. The murderer has decided that justice has not been provided through social and legal means and so decides to dispense justice himself. The difficult question for Christie is how to make the murderer sympathetic without sacrificing law. She does this by making the initial murder an innocent child who suffered greatly. The first victim is the foster mother who was responsible for the child's death. The second victim is the magistrate who placed the boy in foster care. Christie adds to the second victim's appeal as a sacrifice for justice by giving her an unattractive personality. And to stack the deck further against the two female victims, she makes the murderer friendly and attractive, but emotionally and mentally disturbed. Accordingly, the audience is sympathetic to him and uncaring about the victims. In the end, justice has the appearance of having been served: the deranged young man is taken away to be treated and a sympathetic potential victim has been saved.

Order and Disorder
To establish a venue for murder, Christie creates a scenario that dismisses order from the stage and instead establishes disorder. She does this first with the snow storm that strands all the guests. The second step is to remove any chance of communication with the outside authorities. To do this the phone lines are cut, and the house is isolated. Next the detective's skis have disappeared and the audience realizes that the detective is stranded and unable to seek help. And finally, the guests and their hosts begin to fall apart and their veneer of civility is cracked enough for the audience to begin suspecting any or all of them to be a murderer.

Punishment
Modern audiences are conditioned to expect punishment as a response to crime. But for Christie, punishment depends more on circumstance than the crime committed. Although Georgie/Trotter has dispensed his own idea of punishment to his two murder victims, the audience is given ample reason to dislike the victims and like their murderer. The plot makes clear that Georgie is also a victim, and so his removal to a treatment center at the play's conclusion is a resolution the audience endorses. Generally, most audience members will feel that Georgie has suffered a great deal and that he is deserving of sympathy rather than condemnation. A second glance at the play reveals that he has almost claimed a third and more innocent victim, but since Mollie has not been injured (she leaves the stage unhurt and more concerned with her burned pie than her near death), the audience is permitted and encouraged to direct all its sympathy to the young man who was more victim than victimizer.

Revenge
Like punishment, revenge is the motivating force behind Georgie's deception. He is seeking revenge for his brother's death and revenge for the injuries he suffered. The two murder victims are unsympathetic characters, while the murderer is portrayed as both likable and emotionally unstable. All of these elements lead the audience to recognize and sympathize with the young man when he is unmasked at the play's conclusion. Forgotten is the fear and conflict that permeated the last act. But, since the last act takes place only ten minutes after the second victim's murder, presumably, their collective fear was not great. In fact, Christie leaves the audience with an understanding that all the guests are once again engaged in common-place activities.

Sanity and Insanity
Insanity is offered as both a mitigating reason for Georgie's actions and a justification for the murder of two people. Throughout the play the murderer is referred to several times as a homicidal maniac, but the connotation of maniac is someone who is unbalanced. In fact, the definition of maniac is a madman, a lunatic, someone who is violently insane. After Trotter is unmasked as Georgie, the audience, who has come to like the young man, is quick to accept that he is insane. Indeed the conclusion reveals that he is not going off to prison, but instead, he has been sedated and will be confined somewhere for treatment. His insanity is justified by the circumstances of his childhood. And it is a solution with which the audience is comfortable.