SO (spoilers be a comin'). A Lost Lady is a wee little book wherein a Lady marries a Fella. The Fella is old-but-nice-and-honorable and the Lady SEEMS nice but is actually kind of a cheap, silly strumpet. The Fella experiences some financial ruin and soul-crushing health problems but never seems unhappy with the Lady because of his honorable, valiant, never-ending love, etc, etc.
MEANWHILE, a young boy (from whose point of view most of the story is told) grows to idolize the Lady because she is Rich and Pretty and Nice to the Poor Folk. He catches her in all her strumpetness and ALAS, his idol falls to the ground and he is upset. She continues being strumpety until her husband dies, then she moves to South America and marries another rich old man, the end.
(Psst, the Lady is a symbol for the dying valor of the pioneer West as it succumbs to the grubbing hands of icky, tasteless capitalists.) There were a few moments where I, as a modern middle class fan of democracy and egalitarianism, cringed at Cather's classism. It can be a bit, "the boy was aghast at how the Lady let the village boys actually LOOK HER IN THE FACE and EAT HER FOOD when she invited them to dinner, and at how they used the wrong forks despite the fact that their back story included some bits about starving quietly like good poor folk do." Some of those boys grow up to be vulgar and gross, MUCH LIKE THE WEST IS NOW VULGAR AND GROSS DOES EVERYONE GET MY MESSAGE OKAY GOOD.
Aside from the not-so-subtle preachiness of it, I enjoyed this thoroughly. Cather is a master of simple language used to convey the most heartbreaking of things (a literary Thing which is among my favorite literary Things). She lets scenes speak for themselves. She's a master of Show, Don't Tell. If you do read this, don't be surprised if you become a little obsessed with the Fella (the old one with the money and health problems). He's actually the hero here.
Four stars out of your mom