Jem and Scout begin to start finding objects in the knothole of the tree after school. Scout thinks it might be where Walter hides his things. Someone may have a hiding place to hide things from older folks which could impact the plot later. Jem and Walter do the right thing and leave the twine alone until the owner claims it.
After three days, the ball of twine was still in the knothole. So, they decided that they could take it for themselves. They weren't sure who was putting the items in the tree but they didn't think too much of it. We find out that it is not anyone's hiding spot and that someone knows Jem and Scout and is leaving items for them. Jem and Scout write a letter thanking whoever is leaving them things which is very polite.
After a few days of collecting items from the tree, Jem and Scout realize that someone had put cement in the knothole. Jem later asks Mr. Radley if he knew who put cement in the knothole. Mr. Radley explains to Jem that he had put cement in the tree because he claims that it was dying. We find out that the tree cannot be used anymore. Jem and Scout are upset that Mr. Radley had put cement into the tree.