Mary's husband, who she adores and worships, comes home from work and behaves a little bit differently than normal. For one, he downs all of his whiskey, and gets another glass; normally, he just has one drink, and doesn't even get through it very quickly. Then, he gives her some news that is very upsetting. What is interesting about the way that Dahl tells the story is that he doesn't give the details of the news; he merely summarizes the main gist of what the husband says:
"'This is going to be a bit of a shock to you, I'm afraid,'...and he told her. It didn't take long, four or five minutes at the most...'And so there it is,' he added, 'And I know it's kind-of a bad time to be telling you...of course I'll give you money and see you're looked after."
So, we don't get the details--it could have been any number of things, but the bottom line of it all is that she will be left alone. He's leaving her, we just don't know why. We can infer that he's in love with someone else, or not in love with her anymore, but we don't have the specifics. Dahl leaves that up to the reader, to fill in the blanks however they want to. But the details don't change the fact that he has betrayed her, and is completely abandoning her and their unborn child. That is enough to upset anyone, and the shock of it really gets to Mary in this story. I hope that helped; good luck!