The Sign of Four is the second book in the Sherlock Holmes series written by Sir Arthur Conan Doyle. The book takes place in London after the events of the first book. However we do not know how long after the first book. Sir Arthur Conan Doyle did make a few mistakes one of them is where Watson got shot. In the first book Watson was said to be shot in the shoulder but, in the second book Watson was said to be shot in the leg.
Also in the second book we learn that Sherlock takes drugs. In my opinion this Novel is a great follow up to A Study In Scarlet. This book in my opinion has more characters to send Sherlock and Watson on a wild goose chase. That is my review for A Sign Of Four If u want me to do a longer comment on this blog.