On the day of the picnic, Tom and Becky go into the cave with the other children. They quickly get tired of the hide-and-seek game everyone else is playing, and they decide to explore instead. Tom goes behind a waterfall and finds a downward passageway, much like a staircase. The two of them poke around for a while, marking their turns with smoke from a candle. Soon they find themselves in a magnificent world of stalactites and stalagmites. They come into a large chamber and disturb a family of bats, which chase them, putting out Becky’s candle. Tom relights it with his own candle, but when the two of them decide to turn back, he suggests taking a different route. They have no matches, so he does not want to go past the bats and risk losing both flames at once.

Tom investigates a whole series of passages, but does not recognize any of them. He tries to keep Becky cheerful, but she soon realizes that they are lost. Becky suggests retracing their steps, but this does not work. It never occurs to Tom to mark their latest turns with candle smoke; he thought he would find his way forward without needing to turn back. Becky begins to cry. Tom berates himself, admitting it is all his fault they are lost. Becky does not want him to feel this way, so she tries to cheer Tom up.

The children push onward, looking for a way back to the cave entrance. Tom scares Becky by blowing out her candle. While she knows he has a whole candle, plus several pieces of candle in his pocket, she does not want to imagine being stuck in the cave long enough to use them all up.

When the children stop to rest, Becky falls asleep for a while. They share a piece of cake that Tom stowed in his pocket during the picnic. Becky cries again, but Tom assures her that people will miss them and search for them. They quickly realize, however, that Becky is not expected home that night. And because Tom has a bad habit of staying out late, it is possible that neither child will be missed until the following day.

Eventually Tom stops beside a spring and admits that they can go no farther. Their last stub of candle is about to burn out, and they need to stay near water. For a time, he and Becky sit hopelessly in the darkness by the spring. When at last they hear voices calling, they grab each other by the hand and try to make their way toward the searchers. They shout and shout, but the sounds of the searchers fade away. They feel their way back to the spring and wait with increasing despair. They sleep some, and their hunger grows unbearable.

Tom knows that the search will soon end. He is beginning to feel crazy, sitting idly and waiting, and so he decides to try again to find a way out. Using a kite string from his pocket to mark his route, he begins exploring the side tunnels that lead away from the spring. On the second or third try, he enters a chamber and is astonished to see a hand holding a candle. He shouts out in joy—but when he sees the face that is attached to the hand, he cowers and hides: The man in the chamber is Injun Joe. Joe runs away from Tom’s voice. This is lucky, because Tom knows for a fact that Joe will kill him if they meet. Becky, behind Tom, does not see Injun Joe. Tom does not want to scare her, so he pretends he only shouted “for luck.” They make their way back to the spring.

It is a long time before Tom has the courage to go exploring again. By now Becky is so weak and cold that she refuses to come along. She encourages Tom to go by himself, but she asks him to come back often to check on her. She is sure she is going to die, and she makes him promise not to leave her alone when the time comes.