The passages that you are looking for start at the beginning of chapter 27. A few paragraphs in, Lee alludes to the fact that Bob Ewell is on the rampage; he is upset that his reputation has been ruined by Atticus's adept questioning in the courts, and wants to enact revenge. So, he starts with Judge Taylor, who Bob also felt slighted by, as the Judge was not very polite to him during his testimony. One night as the Judge was reading the paper, he heard a "scratching noise...from the rear of the house." When he went to investigate, "the screen door [was] swinging open" and a shadow was lurking in the corner of the yard. So, Judge Taylor went back to reading, but this time "with a shotgun across his lap." So, nothing too drastic there, but, Bob was making his presence known.
As for Helen, she was fortunate enough to receive a job from Tom's former employer, Mr. Link Deas. The book states,
"He didn't really need her, but he said he felt right bad about the way things turned out."
However, to get to work, she had to go a mile out of her way to avoid the Ewell place, because they were rude and threatening to her. Deas finds out about this, and "walked Helen home" that day, stopping to threaten the Ewells. He shouts out to Bob that if he bothers Helen again, he'll "have [him] in jail before sundown." However, Bob follows Helen to work the next day, whispering insults, to which Deas tells him he'd better knock it off; Bob listens this time and leaves her alone.
So, Bob makes mischief for both Helen and Judge Taylor, but fortunately, no lasting damage is done. Yes, he is saving that up for later in the book, as you'll find out. I hope that helped!