How do Tom and Becky escape out of the cave

That night, Tom told the entire story of their adventure to an eager audience: how he had left Becky and went exploring the cave; how his kite-line had stretched as far as it could go; how he was about to turn back before he spotted a "far-off speck that looked like daylight." Pushing through a small hole in the cave wall, Tom had been able to see the Mississippi River and was able to return into the cave to save Becky.