The Adventures of Sherlock Holmes
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In and of themselves, they're a good selection, with Holmes bending his mind to cases that confound the police.
But, this is also the downside to them. Once you've read the book a few times, you aren't thinking "gosh, how does he do it?", you're just thinking how can everyone else be so dense. The stories stop being clever after that point.
Good if you're a fan of the characters, stories or the many TV adaptations.
Good for an enjoyable read on the train.