The Valley of Fear by Arthur Conan Doyle. Short summary

5 seconds

A spy is infiltrated into a Masonic order of assassins. The Masonic organization is destroyed, but many years later, the surviving villains kill the spy.

1 minute

Holmes receives an encrypted message from Moriarty’s man. At the same time, he learns that its owner, Mr. Douglas, has been murdered at Birlstone Manor. Suspecting that Moriarty is involved in the case, Holmes and Watson go to the scene of the crime.

Mr. Douglas has been shot at point-blank range, so the face cannot be identified. Holmes comes to a conclusion that another man is killed. It turns out to be an old enemy of Mr. Douglas, who looks like him.

Holmes cunningly lures the hiding master Birlstone out of the house. Douglas writes down his story and gives it to Dr. Watson.

Once upon a time, he, worked as a detective. Under the name of John McMurdo, he infiltrated a Masonic order of assassins. All of its members were arrested and executed, except one. To avoid his revenge, the detective becomes Mr. Douglas and goes to England.

Soon Holmes learns that Douglas has been murdered. He suspects that it is the work of Moriarty.