To Kill A Mockingbird
The plot was the Boo Radley mystery plot line. The reason is because Jem's conversation Mr. Radley said,
'"Yes," he said, 'I filled it up.'
'Why did you do it, sir?'
'Tree's dying. You plug'em with cement when they're sick. You ought to know that, Jem"' (pg 83), but after we find "Jem asks Atticus 'Is that tree dyin'?'
'Why no, son, I don't think so. Look at the leaves they're all green and full, no brown patches anywhere—'
'It ain't even sick?'
'That tree's as healthy as you are, Jem'" (page 84).