How does Dahl use irony to bring back humor to the plot?
Humor is brought back into the plot by the ironic conclusion: the officers are eating the murder weapon. Yet, they are so sure they will find it and catch the murderer. But Mrs. Maloney is getting away with the perfect crime, which adds to the irony too. Initially she appears to be the typical subservient housewife of the time period. However, once her husband states that he is going to leave her, despite her pregnancy, and she murders him, Mrs. Maloney begins to transform. She changes from that obedient wife to a strong female character who is taking full control of her life. This adds to the humor of the tale as the male officers, who were co-workers of the murdered husband, are sure they will catch whoever did it. Yet, there is Mrs. Maloney smiling at them as the quickly gobble up the murder weapon and help her get away with the crime.
The story starts tame, gets serious, then lightens up in the end. When Mary kills her husband and coldly goes about the business of covering it up, there is an eerie and off-putting feel to the story. However, the ironic scene of the policemen eating her prepared leg of lamb dinner - in other words, eating the murder weapon - and commenting that the answer must be "right under their noses" allows readers a light-hearted ending to what could be a troubling story.