Sherlock: The Casebook is a companion piece to the BBC television series starring Benedict Cumberbatch and Martin Freeman. It was written by Guy Adams and released in 2012, at 160 pages in length.

The Casebook details the first two seasons, or six cases, of the show. They are as follows:

-A Study in Pink
-The Blind Banker
-The Great Game
-A Scandal in Belgravia
-The Hounds of Baskerville
-The Reichenbach Fall

Each chapter focuses on a separate case, in the order in which they appeared on the show. They're examined through Watson's point of view as he writes his blog, which is very clever on the author's behalf! Watson delves further into each case to explain them in more detail, often trying to grasp how Holmes figured out the little things.

This book also includes information about the original stories that they're based on, as well as the hidden references, or "easter eggs", they've written into each episode. Cleverly, Sherlock will cut in with his point of view on each case via little notes, often berating Watson in some way or another.

While this is by no means a necessity, this is a great little book if you're a diehard fan and love collecting anything to do with Sherlock. I personally enjoyed it, and I hope they release a second casebook to discuss cases 7-12.