Mischief
Mischief is the dominant theme in "The Lumber Room." From the beginning to the end of the story, Saki delights the reader with Nicholas's persistent playful misbehavior. In the opening scene, the narrator details how Nicholas complains of a frog in his breakfast bowl, only to reveal that he put it there himself. His antics land him in trouble with his authoritarian aunt, but Nicholas's bottomless capacity for mischief means he uses the punishment of having to stay home to his advantage. While the other kids go to the beach and his aunt stands watch at the entrance to the gooseberry garden, believing Nicholas will try to sneak in, Nicholas is free to act on his long-awaited plan: entering the lumber room. Having satisfied his curiosity, Nicholas goes back to the garden when his aunt calls his name. She is stuck in the rain-water tank and needs his help to get out, but Nicholas can't pass up the opportunity for further mischief. Instead of getting the ladder, he reminds her that he is forbidden from going into the gooseberry garden. He then pretends he believes she isn't his aunt, but rather the Devil trying to tempt him to misbehave. Ultimately, Nicholas's penchant for mischief makes the boredom of living under his aunt's rigid control bearable.
Imagination
Imagination is another of the story's major themes. Alongside mischief, Nicholas shows a great capacity for imagination. Although Nicholas uses his imagination in order to devise plans to carry out mischief, the theme comes up even more explicitly when Nicholas enters the lumber room. Long prevented from seeing the treasures that lie within, Nicholas imagines the otherworldly potential of the restricted room, which "[comes] up to his expectations." Inside, he finds a fire-screen tapestry that depicts a scene frozen in time. A bow huntsman and his dogs stand before a dying deer, and Nicholas imagines what will happen if the huntsman does not notice the wolves stalking toward him from the woods. He also finds a book of bird illustrations. When he hears his aunt shrieking his name, Nicholas is busy "assigning a life history" to a mandarin duck.
Nicholas also uses his imagination once he is outside and tasked with helping his aunt escape the rain-water tank. Thinking quickly, he invents an excuse not to help or trust her, pretending she is the Devil. At the end of the story, when everyone sits in miserable silence at the tea table, Nicholas continues to use his imagination to his benefit, thinking back to the tapestry scene and imagining alternative outcomes for the huntsman and his dogs.
Authority
In contrast to Nicholas's playful mischievousness and imagination is his aunt's oppressive imposition of authority. The theme of authority arises in the story's first sentences, when Saki sets up the premise: "The children were to be driven, as a special treat, to the sands at Jagborough. Nicholas was not to be of the party; he was in disgrace." The narrator's passive voice obscures the role the aunt plays in the punishment, but the narrator later explains how it is the aunt's decision to keep Nicholas home; in fact, she invented the occasion of the beach trip explicitly to punish Nicholas for putting a frog in his breakfast bowl. The aunt continues to flex her authority over Nicholas, barring him from the gooseberry garden while he is grounded. In a passage that reveals how strongly she believes in her authority, the aunt says, "It’s no use trying to hide there; I can see you all the time," although both the reader and Nicholas know how wrong she is. The aunt's oppressive authority eventually comes back to haunt her when she needs Nicholas's help to escape the rain-water tank. Having cultivated a hostile power dynamic with the boy, the aunt discovers that when the tables are turned and she is at Nicholas's mercy, he is especially unlikely to obey her command.
Defiance
Defiance is another of the major themes in "The Lumber Room." Expressed predominantly through Nicholas's reactions to his aunt, defiance first arises as a theme when the aunt tries to impose restrictions on Nicholas's freedom. Hoping Nicholas will cry because he has been left out of the beach trip, the aunt is dismayed to see that Nicholas defies her expectations by chuckling at the sound of his cousin crying in the carriage. Defiance comes up again when the aunt disallows Nicholas from going into the gooseberry garden. Nicholas has an obstinate expression that makes the aunt certain he will try to defy her command, and Nicholas proceeds to exploit her expectation of defiance by pretending to try to get into the garden. With his aunt distracted, Nicholas is able to safely enter the restricted lumber room and enjoy its treasures. As a final act of defiance, Nicholas refuses to help his aunt when she gets stuck in the rain-water tank. In an instance of situational irony, he refuses to fetch a ladder on the grounds that he must obey his aunt's initial command to stay out of the gooseberry garden, effectively defying her through obedience.
