The Cross-Time Engineer

This is one of those books in which a modern man is suddenly transported into the past, and manages to make something of himself by exploiting all the things he knows that the people around him don't. There's a whole family of such books, going back to [b:A Yankee at the Court of King Arthur 13793031 A Yankee at the Court of King Arthur Mark Twain https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1337245571l/13793031.SY75.jpg 2621763], and in general I like them if they're done well.The hero, Conrad, is a Polish engineer unexpectedly transported back to Poland in the year 1231 AD. The Polish language has been stable for a long time, so he doesn't need to relearn it; and, being an engineer, he knows some useful things. But he also knows that the Mongols are going to invade in ten years and kill everyone; so he has a strong motivation to try to do something about that.It's a good scenario, and Frankowski depicts Poland in 1231 quite plausibly. Initially Conrad spends most of his time and energy trying to industrialize Poland, which involves a variety of engineering projects but also social and business innovations. He gains some initial capital in various ways, and builds up a profit from his innovative activities. He's fortunate to gain the support of a few members of the aristocracy (although others are suspicious or hostile).In his spare time, he likes to have sex daily, and preferably with a variety of different women (marriage doesn't attract him). He finds that the age of consent in that time and place seems to be 14, and takes full advantage of that. He has only consensual sex, and in his own way he treats women kindly and considerately; but he's promiscuous by inclination, and women seem to find him attractive.The whole story seems to be the author's wish-fulfillment fantasy, fully worked out and written down in detail. Although Conrad does encounter problems and setbacks now and then.Overall, I find the story mildly entertaining in places and mildly tedious in other places. I'm no engineer, so the engineering projects are much more interesting to the author than to me. Conrad's sexual activities (which are not described in intimate detail) are presumably enjoyable for him, but do nothing for me. The social interactions and his project of gradually upgrading the whole country are of some interest.This book is the first part of a series (there are sequels), so it ends at an intermission point rather than a true dramatic finish. You can decide whether you want more; some will, some won't.It's probably suitable only for people who normally read sf, and not for a general audience.