Mrs. Foster has had "an almost pathological fear of missing a train, a plane, a boat, or even a theatre curtain," according to the narrator. Her husband is a secret sadist. He torments her by creating countless deliberate delays. But she is not aware of what he is doing until the day they are closing up their townhouse in Manhattan and she is flying to Paris to visit her married daughter for a full six weeks, while he intends to stay in New York and live at his club. Their car is waiting to take this affluent elderly couple first to the airport and then to Mr. Foster's club. But he is deliberately stalling, as he usually does when she is anxious about being late. This time he goes back into their house on the pretense of wanting to get a few cigars. She is sure to miss her plane, and it is of the utmost importance to her. Then when he comes back he tells her he had a little package he wanted her to take to their daughter in France, and he gets out of the car again.

Mrs. Foster comes to realize that her husband has been torturing her for years with his little tricks. 

At this point, Mrs. Foster suddenly spotted a corner of something white wedged down in the crack of the seat on the side where her husband had been sitting. She reached over and pulled out a small paper-wrapped box, and at the same time she couldn’t help noticing that it was wedged down firm and deep, as though with the help of a pushing hand. “Here it is!” she cried. “I’ve found it! Oh dear, and now he’ll be up there for ever."

They live in a tall, narrow townhouse. Because there are six floors and they are old, they need a little elevator to get up and down. When Mrs. Foster goes to the front door she hears from outside that her husband is riding up on the elevator. But then she hears something else.

She appeared actually to be moving one of her ears closer and closer to the door. Now it was right up against the door, and for still another few seconds she remained in that position, head up, ear to door, hand on key, about to enter but not entering, trying instead, or so it seemed, to hear and to analyse these sounds that were coming faintly from this place deep within the house.

Then, all at once, she sprang to life again. She withdrew the key from the door and carne running back down the steps.

“It’s too late!” she cried to the chauffeur. “I can’t wait for him, I simply can’t. I’ll miss the plane. Hurry now, driver, hurry! To the airport!” 

She stays in Paris for six weeks, and the townhouse supposedly remains totally empty for all that time. The author does not reveal what it was Mrs. Foster heard until she gets back from Paris at the end of the story. Then she has to dial a number and has the following conversation over the phone.

“Hello,” she said. “Listen - this is Nine East Sixty-second Street . . . . Yes, that’s right. Could you send someone round as soon as possible, do you think? Yes, it seems to be stuck between the second and third floors. At least, that’s where the indicator’s pointing."

Obviously what she had heard six weeks before was the sound of their elevator getting stuck between floors while Mr. Foster was riding up on the pretense of going to look for the little white package which he had deliberately left jammed down beside the seat in their car. Mrs. Foster had then and there decided that she had a golden opportunity to get her revenge for all the years he had tormented her. All she had to do was stay in France and assume that her husband was living at his club in New York. The people at his club wouldn't miss him because they were not expecting him. The author, Roald Dahl, had disposed of the question of their corresponding with the following brief dialogue:

“Will you write to me?” she asked.

“I’ll see,” he said. “But I doubt it. You know I don’t hold with letter-writing unless there’s something specific to say.”

The reader can imagine what the elevator repairman will find when he gets there. Mr. Foster will be a shriveled corpse. There will be signs that he had desperately tried to get out of the little elevator but that he was hopelessly trapped and finally died of starvation. He will have gotten what he deserved for his "passive aggression," his fiendish targeting of his trusting wife in the area where she was most vulnerable. Mrs. Foster had used the same "passive aggression" to get her revenge. All she had had to do was to do nothing.