Most of Curwood's stories were adventure tales set in the Canadian North, where the author spent much of his time. During the 1920s his books were among the most popular in North America, and many were made into movies. The River's End was the first book to sell more than 100,000 copies in its first edition. The book begins: Between Conniston, of His Majesty's Royal Northwest Mounted Police, and Keith, the outlaw, there was a striking physical and facial resemblance. Both had observed it, of course. It gave them a sort of confidence in each other. Between them it hovered in a subtle and unanalyzed presence that was constantly suggesting to Conniston a line of action that would have made him a traitor to his oath of duty. For nearly a month he had crushed down the whispered temptings of this thing between them.