Four signatures, also known as four signatures. It is the second mystery novel written by arthur conan doyle, a British detective novelist, after The Study of Blood Characters, with Sherlock Holmes as the protagonist. The story takes place between 1887 and 1888. It tells the story that mary morstan, a British lady, receives an anonymous parcel every year after her father disappeared. It turns out that there is a conspiracy. This novel objectively exposed and reflected the British colonial activities in India, and it was a great success once it was published. At the same time, the author is also famous for it. In addition, there are many film and television works of the same name.