In the first episode of a series that explores the books we (really) read, Andrew Marr investigates the curious case of detective fiction. This is a genre that been producing best-sellers since the 19th century, and whose most famous heroes - Sherlock Holmes, Hercule Poirot, Inspector Rebus - are now embedded in our collective psyche.

What is it about stories of magic, epic adventure, and imaginary worlds that has turned fantasy fiction into one of the world's most popular forms of storytelling, regularly filling the bestseller lists and entrancing adults and children alike?

What is the allure of the classic espionage story? As Andrew Marr argues in the conclusion to his series about the books we (really) read, the British spy novel is much more than a cloak-and-dagger affair.