The mood of the story is one of surrealism and black humor. Here is an old man selling love potions and undetectable poisons in the wide open in a shop in modern Manhattan. He must be well known because he has been recommended to the young man who enters.
"Is it true," asked Alan, "that you have a certain mixture that has--er--quite extraordinary effects?"
New York is such a big and populous city that it just seems remotely possible that there could be someone somewhere who would be dealing in love potions and undetectable poisons. The old man knows what Alan Austen is looking for, but he introduces a different item immediately.
"Here, for example," interrupted the old man, reaching for a bottle from the shelf. "Here is a liquid as colorless as water, almost tasteless, quite imperceptible in coffee, milk, wine, or any other beverage. It is also quite imperceptible to any known method of autopsy."
Throughout the story the old man makes allusions to this colorless liquid. He calls it a "glove cleaner" and a "life cleaner." He is not much interested in selling Alan the love potion which the young man so urgently desires. The profit the dealer expects to make will all come from the poison when, as he fully anticipates, Alan gets bored with marriage and wants his freedom. The love potion costs just one dollar, but the "glove cleaner" or "life cleaner" will cost
". . . five thousand dollars, never a penny less. One has to be older than you are, to indulge in that sort of thing. One has to save up for it."
He obviously expects the love between Alan and the girl named Diana to last for some years, during which time Alan will move up in the world financially and will be able to afford the expensive poison when, as the old man predicts, he becomes tired of his wife's possessiveness and togetherness.
Characteristically, John Collier treats his subject with a strong touch of humor. Also characteristically, he shows a very cynical attitude about love and marriage, probably based on his own experience. In this respect he resembles Ambrose Bierce, who defined marriage in his book The Devil’s Dictionary (1906) as:
The state or condition of a community consisting of a master, a mistress and two slaves, making in all, two, and defined love as A temporary insanity curable by marriage or the removal of the patient from the influences under which he incurred the disorder.
When Alan thanks the old man for the love potion and says "Good-by," the old man replies, "Au revoir," which literally means "Until we meet again." He fully expects his new customer to make a return visit in the future and to pay him the five thousand dollars for "the chaser." The words "Au revoir" can be regarded as yet another allusion to the poison as well as an allusion to marriage.
The mood of the story, as well as being surrealistic, is humorous and sardonic. Collier does not expect his story to be taken seriously. Men do not normally poison their wives if they get tired of marriage, but Collier makes it seem as if this is the natural thing to do. Why not just get a divorce? Well, if Alan became prosperous during the honeymoon years of marriage, it might be cheaper to pay five thousand dollars for the poison--as Collier and the old man imply--than to pay attorney fees, split the community property, and pay alimony indefinitely.