Tommy Barnes appears as a minor character during the formation of Tom Sawyer's Gang. He is the youngest participant gathered at the cave. While the other boys eagerly discuss plans for robbery and murder inspired by adventure stories, Tommy falls asleep during the proceedings.

Awakened later, Tommy becomes frightened and emotional. He pleads to return home to his mother and declares he no longer wants to be a robber. This reaction draws taunts from the other boys, who mockingly call him a "cry-baby," further upsetting him. In his panic, Tommy threatens to expose the gang's secrets.

To prevent this potential betrayal, Tom Sawyer intervenes, offering Tommy five cents in exchange for his silence. This payment secures Tommy's temporary compliance and halts his immediate protest. Tommy's presence and actions illustrate the contrast between the younger boy's grasp of the gang's activities and the older boys' romanticized notions of adventure drawn from fiction. The incident underscores the group dynamics and Tom Sawyer's role as a manipulative leader who resolves disputes through bribes.