Madame Bovary is about a doctor's wife in a small French town who tries to alleviate her ennui by shopping and cheating on her husband.
Her husband - Charles - is kind, but rather dull and unambitious. She cheats on him with fuckboys - then known as dandys.
The Bovarys aren't poor. Mme. Bovery received a small inheritance and Charles makes a decent income as a doctor. But, the combination of Charles' lackadaisical work and collection habits with his wife's propensity for buying fripperies on credit and paying for trysts with her fuckboys plunges them into a difficult to escape cycle of debt.
Overall I thought it was an enjoyable enough book but I don't get the hoopla. The plot caused quite a stir in the 19th century, but by modern standards it's pretty tame. Flaubert did, I guess, pioneer the trope of the housewife who feels bored by her ordinary life and stifled by social convention. But it's a story that's been retold so many times now that it feels rather trite, even though it was arguably innovative at the time.