Considered one of the foundational texts of English detective fiction, Wilkie Collins' The Moonstone is one of those books that you just know you'll have to read someday if you enjoy that genre. I've used it as my "backpack book" in recent weeks (the one I have with me all the time and pull out when I have a free moment on the T or between classes or for the last few minutes of a lunch hour), and found it hard to resist pulling out at home when I should have been working on other things.
This book deserves its place among the foremost examples of detective literature. T.S. Eliot called Collins' novel "the first, the longest, and the best of Modern English detective novels" - while I doubt it continues to hold the middle distinction, The Moonstone may still have a lock on the other two. Conan Doyle, Poe and Collins form, for me, the great triumverate of this genre; I'd be hard-pressed to choose my favorite among them (Collins' The Haunted Hotel is another fascinating early book of this type that I quite recommend).
The Moonstone is the tale of a great Indian diamond which goes missing from the chambers of its young English owner. The search for both the culprit and the diamond, told from the perspectives of various characters, form the basic plot. The suspense doesn't end until the final pages, and the pacing (done as it was for weekly installments) is wonderfully done. Collins' characters are wonderfully memorable, from the erstwhile and Robinson Crusoe-obsessed retainer Gabriel Betteredge to the mystifyingly coy Detective Sergeant Cuff and beyond.
This is a book to savor; if it's been sitting on your shelf awhile, pull it down and read awhile. I'm willing to bet it won't take you long to get hooked.