I spotted copies of these books over at our friends some months ago: I couldn't help but be intrigued since I am a bit of train fan (not to the extent that I'm a gricer but you can't help but be charmed by a steam train, or old fashioned trains generally).
So I bought copies of the first couple of Edward Marston novels about Inspector Robert Colbeck, The Railway Detective and The Excursion Train. There are now SEVEN books in the series and I'm on the fourth Robert Colbeck drama.
They're full of period detail, plenty of nerdy information about trains, and have some smart plotting as well. Great characters too. Highly recommended.