Many argue that John Buchan's The Thirty-Nine Steps (originally published as a serial in August and September 1915 in Blackwood's Magazine) is one of the most influential thrillers ever written. The novel follows Richard Hannay after his return to London from a trip to South Africa. Initially, he is incredibly bored when he gets back, but when he learns of an assassination plot that could devastate the political balance of Europe, his life becomes very complex. Pursued by the police, he flees to Scotland, along the way trying to figure out what exactly the 39 steps are and how they relate to the assassination plot -- if they do at all.
On Amazon, The Thirty-Nine Steps has a respectable rating of 4 out of 5 stars, with many calling the novel a "thrilling adventure." On book review aggregator Goodreads.com, it holds a similarly solid rating of 3.61 out of 5 stars. When it was released, the Telegraph called the novel "one of the finest thrillers ever written." It usually places on lists of most-loved novels in the United Kingdom. The novel was adapted four times into film, perhaps most famously in 1935 by famed auteur Alfred Hitchcock. That adaption was met with critical acclaim and is regarded as a masterpiece. It was also adapted into a video game, the theater (where it won a number of Tony Awards and was last performed in 2010), and into radio by Orson Welles in 1939.