What does the last sentence in Chapter 10 mean? What happened?
What the last sentence in this chapter means is that Tom Sawyer's heart is broken. Finding the brass andiron knob lying there was the last straw. It was the thing that (when added to all the other stuff) finally broke his heart.
He is sad by the end of this chapter for a couple of reasons. One thing that is going on is that he is really worried about the whole deal with Injun Joe and Muff Potter. That is kind of making him gloomy.
The other thing is his "love life." When he finds the knob, he knows for sure that Becky doesn't love him anymore. he knows that because it was his prized possession and he gave it to her as a token of love. So if she left it on the floor...