Themes are ideas that run all the way through a literary text. By analysing them you can better understand the writer's intentions. What choices have they made? Why? What are they trying to get you to think and feel? Analysing themes allows you to write extensively about a literary text.
In The Sign of the Four there are many themes which could be analysed. For example:
These themes are presented through the characters and the layered plot. Other ideas that are dealt with include betrayal, greed, and chance. The Sign of Four is a detective story, written and set in late Victorian times. In his Sherlock Holmes stories, Sir Arthur Conan Doyle establishes the conventions of the modern detective novel, in which a rational and intellectual central character investigates and ultimately solves a mystery.