In the beginning of the story, the old acquaintances (she was the old lady, the mistress of the house, and he was a very old friend of hers) were sitting in front of the fireplace when a log fell out from the fireplace into the drawing-room and rolled on to the carpet. That reminded him of an event from his youth which had given him a kind of prejudice against marriage.
Here is his story.
He had a friend who decided to marry. Their friendship continued, the spouses invited him to dinner and other family's events.
Once, at the request of the wife, he was invited to their house to entertain her while her husband (his friend) had to come back home late for business deals.
When he came and stayed one on one with that woman, embarrassing silence hung in the air. She started the conversation from the question about love, finishing it with a hint that she might be in love with him. She said that the fireplace in front of which they were sitting was rather hot and suggested moving to the sofa. He reluctantly followed her and suddenly she gripped his head and kissed him. The author made this remark: "Let the man who has never felt on his lips the warm kiss of a woman who is ready to give herself to him throw the first stone at me."
This intimate moment was interrupted "... when a loud noise made us both jump up. The log had fallen into the room, knocking over the fire irons and the fender, and on to the carpet". When he threw the log into the fire, the husband unexpectedly came back, much earlier than they expected. Thanks to this log the terrible disclosure didn't happen.
Nevertheless, since then, the family began to avoid meeting with him and he came to an unpleasant conclusion about faithfulness, love, and relationships. He never married.
It is an interesting to see in the story not only action. I noticed, that the author put into the story some interesting observations.
Testing relationships by silence:
If people feel comfortable in silence, it proves their good relationship. We can see an illustration of it in the beginning of the story: "They had not spoken for about a minute, ... dreaming of no matter what, in one of those moments of friendly silence between people who have no need to be constantly talking in order to be happy together"
An opposite feeling we can see in the last part of the story which proved that if people didn't have a good relationship, the silence became tense. The main character of the story named it "that painful silence"
About relationships between man and woman the author said:
" ... a man and a woman are always strangers in mind and intellect; they remain belligerents, they belong to different races. There must always be a conqueror and a conquered, a master and a slave; now the one, now the other--they are never two equals."
The definition of love according to the woman who was ready to betray her husband:
"It seems to me that real love must unsettle the mind, upset the nerves and distract the head; that it must--how shall I express it?--be dangerous, even terrible, almost criminal and sacrilegious; that it must be a kind of treason; I mean to say that it is bound to break laws, fraternal bonds, sacred obligations; when love is tranquil, easy, lawful and without dangers, is it really love?'"
Summing up, I would like to note that the true Master includes into his masterpiece something that reader has already known. It makes some plot lines very recognizable and memorable. So Guy de Maupassant did.
Here are the links to the text and audio of this short story: