This is an excellent short story, and it will not take you much time to read it, so please don't use this summary as a substitute for reading it yourself.
The story opens with the sight of an army lieutenant rationing out the coffee supply his company has. A sudden shot sounds and the soldiers see blood covering the sleeve of their lieutenant. The lieutenant tries to sheathe the sword he had been using to count the coffee packets as his mind is overwhelmed by the mysteries of life and existence. His soldiers try to assist him and he leaves the field overwhelmed by sadness to seek medical assistance.
As the lieutenant moves towards his goal, we are shown a series of wartime vignettes: horsemen in the midst of motors, wheels and levers, an aide galloping to a general and delivering a message, and batteries moving forward intent on destruction. The drama of war is shown through these sights, as is the adventure of war demonstrated through the roadside brigade that is making coffee and chatting "like girls at a boarding school."
As he arrives at the hospital, a surgeon greets him initially with kindness, but then when he sees the wound of the lieutenant, he treats him with contempt, ordering the lieutenant to accomapny him. He then tries to encourage the lieutenant to come with him by lying to him and saying that he will not amputate the arm. The lieutenant finally goes with him towards the entrance to the tent, which to him looks like "the portal of death." We are told that this is how the lieutenant had his arm amputated.
The last section of the story describes the sadness of the lieutenant's family at the sight of his sleeve that is empty. However, we are told that in reality this event is nothing, just something that many soldiers experienced and just another "episode of war."