The Seven-Per-Cent Solution, by Nicholas Meyer

This was a best-seller back in 1974, and boy does it feel like it. Sherlock Holmes is lured to Vienna by Watson in order to get treatment for his cocaine addiction at the hands of Sigmund Freud; together they solve the mystery of a lost heiress and prevent Europe from falling into war before its time. There is a thrilling chase sequence on two steam trains across Austria. That's about it, really; every generation updates Holmes for its own age, perhaps, and this was the 1970s version. I'll stick with Cumberbatch, Freeman, Gatiss and Moffatt.