Arms and the Man is a play for the theatre. It is a social commentary on war, military values, and manners in the upper class. It was Shaw's first effort for the stage, and did not enjoy success critically or financially initially, but it has become quite a famous and often-performed play.
The plot of the play is broadly thus: A Serbian soldier in the Serbo-Bulgarian war takes refuge in the bedroom of young Bulgarian lady named Raina. She is engaged to a Bulgarian officer named Major Saranoff, whom Raina has just heard has distinguished himself in the latest action. Raina is kind-hearted, however, and does not give away the whereabouts of this enemy fugitive. Raina and her mother are kind to the soldier, who is scornful of military honor and glory, and seems to think only of avoiding harm to himself and others. They keep his visit hidden from the rest of the family.
The war ends, and Raina's father returns home. Raina's father denigrates Raina's fiance's prowess as a military leader; then that young gentleman comes for a visit. There is a discussion about a young Swiss soldier (fighting for the Serbians) taking refuge in the house of a Bulgarian. Raina and her mother Catherine now know that the story of their harboring a soldier has become known, though no one knows that it was indeed them who hid the enemy.
Raina and Sergius Saranoff are reunited, and their emotions are syrupy and insincere. Sergius has an obvious attraction to the maid, Louka. Catherine and Raina's subterfuge is almost found out, when the coat that they lent to the soldier is requested by Raina's father. Then the man they harbored, now revealed to be a Swiss army officer (who had fought on the Serbian side) named Major Bluntschli, comes to return the coat. Raina and Catherine try again to conceal their previous acquaintance with him.
The coat is duly found, placed again in the closet where it was supposed to have hung all along. Raina's father does not appear to have noticed the subterfuge. When Raina and Bluntschli talk she tells him she left a note and a portrait in the coat for him; he never found it, which means these incriminating bits of evidence are still in the coat pocket. In the course of this act it becomes clear that Saranoff loves Louka, and Raina loves Bluntschli, so the initial engagement of Saranoff and Raina is now in trouble. Raina's father is prevented from finding the incriminating photo, but he knew of it all along. Raina's father reveals the deception, and it becomes clear which couples love each other. Bluntschli tells everyone that he is a rich man, so it becomes possible for Raina to marry him, and Saranoff to marry the maid. On this ridiculous note the play ends happily.
While it is not always easy to discern Shaw's meaning from the play, this is definitely an anti-war play. The long-held notions of military glory and honor are all shown to be silly and counter-productive, and pacifism and a certain cynical self-interest are held to be more sensible. The comedy is sometimes scathing, but the overall play is light-hearted. Arms and the Man has become a classic.