John Marcher has a premonition. He calls it his Beast in the Jungle: something, an unknown something, will happen in his life, at an unknown time, in an unknown way. It may be terrible. It lurks in unknown places, ready to spring at any moment. He shares this premonition with his friend May Bartram, and they agree to watch together for the mysterious thing about to happen. To say much more will spoil the story.

The story, as with many of Henry James' works, takes place primarily in the mind and thoughts of Marcher. It's hard to say more without giving away what the Beast in the Jungle is for Marcher, or of how it ends, but I did enjoy the story.