The Collapse -- economic, leading back to the Iron Age to some extent -- killed a lot of people and there are few left now and they're suspicious with guns at the ready. Jeebee was working on a mathematics team that predicted the Collapse, but not early enough to stop it. He has equations that will help the country get back on its feet, and he's on his way from Illinois to his brother's ranch in Montana so he can save the equations for use in a century or so.
Along the way, he has a lot of bad adventures, but he's joined by a wolf who teaches him how to live in the wild. At one point, he happens on a giant wagon with a sign that says they're traders and he warily contacts them, wanting to trade gold coins for things he needs. After everybody puts guns down, he agrees to work with the traders to make what he needs for supplies because gold coins aren't worth much these days. The head trader's daughter, Merry, and Jeebee are mutually attracted, but he must leave for Montana and she must continue with her father.
Jeebee realizes he won't get to Montana before winter, so he finds a place to settle in for the winter. He gets mauled by a bear and manages to secure his pack and the horses before he takes Dilaudid and antibiotics and passes out. One day, in blowing deep snow, he discovers Merry walking. Really. This was my big problem with the book. An unbelievable coincidence. They have some more tough times, but at the end of the book, everything is fine.
Now, the rest of the book group was very upset that a mathematician would be able to set a door & frame in a cave wall, make a fence, (after lessons from a trader) use a forge, and after being mauled by the bear, was able to secure the pack & horses. I was well at Jeebee's age and I could have done all those. I did similar things at that time. As to being able to do essential things in extreme pain, well, I do that now. Then I collapse. I think the group just assumed an academic wouldn't be able to do these things.
If you can get over the big. massive. coincidence. Read the book.