If you haven’t been introduced to Bernie Gunther, a Jew who is also a former official of the SD and SS (you have to read the book to work that out) turned post-WW2 private eye, then this is the book to start with. It may not be Kerr’s first book, according to the flyleaf, but it is the book in which Bernie starts out his post-war career, so if you read one of his other books first you’ll be a bit frustrated not having the back story.
The One from the Other provides a credible (I have no grounds for saying “authentic”) description of the chaos in occupied Germany in the years immediately after WW2. Bernie has the good fortune to be regarded as someone who can be trusted, even if he is a former Nazi official. Well, in fact, and much to his chagrin, it is mostly former Nazi officials who seek him out to take care of little inconveniences. A favor turns into another which bodes well for turning into a regular practice, and although he would much rather not deal with the former regime there isn’t a lot of employment in a non-existent economy, especially when your only asset is a hotel in the town of Dachau. Bernie never explains why that is: if you’re not up on your history, it was one of the death camps, and the horrors are recent enough that it hasn’t become a memorial. And his wife has a major illness. Like it or not, the paychecks are needed.
I’m not going to spoil a very fine read by telling you how it all works out, although the fact that there are a dozen or so books in the series tells you what the ending will not be. As with any good potboiler there are fisticuffs, near-death experiences as well as encounters with corpses, and a bit of romance, but it is all done rather tastefully so you can let your older teens read it in reasonable safety.
If you get started on this series you’re going to want to get the rest of the books which are, if anything, a little deeper. So get started.