What is the tone in chapter 28 of To Kill A Mockingbird?

This is the chapter in which Jem and Scout are attacked as they cross the dark schoolyard on their way home from the pageant. The tone is ominous. It is a tone of slowly building tension and confusion. Even after the attack happens, the tension and confusion do not completely dissipate. They continue until the end of the chapter, when we find out from Mr. Heck Tate that Bob Ewell attacked the children, and that Bob Ewell has been stabbed dead.
The ominous tone is created against a homey backdrop. There is humor in the first few pages of the chapter, when Mrs. Merriweather narrates her overblown pageant about Maycomb County, and Scout blunders onto the stage, late, in her ham costume. Before the children even get to the pageant, Harper Lee has already given us clues this will be a scary evening.  
On the way to the school, walking by the old Radley place, Jem and Scout discuss how they used to be scared of Boo Radley and haints. Scout, in her narration, adds, "Haints, Hot Steams, incantations, secret signs, had vanished with our years as mist with sunrise." Yet, the next moment she tells Jem to "Cut it out" when he talks about haints. A moment later, she trips on a tree root (foreshadowing what will happen later). There is some discussion about how remote the old oak tree is from all buildings except the Radley place, and how dark it is under the tree. Cecil Jacobs then jumps out and scares Jem and Scout. This is the classic "decoy" jump scare that sets us up for the real thing later. 
After the pageant, the two children begin to walk home across the schoolyard by themselves. Tension and confusion are taken up a notch because Scout, who is narrating the story, is still in her ham costume and can't see out of it. Jem is leading her. Then the tension builds rapidly as the children begin to hear someone following them. There are many little phrases in this section to give us a clue that something is not right:
"I felt [Jem's] fingers press the top of my costume, too hard, it seemed."
"'Be quiet,' he said, and I knew he was not joking."
"This was the stillness before a thunderstorm."
"'Aw, it's just Halloween got you. . . ' I said it more to convince myself than Jem, for sure enough, as we began walking, I heard what he was talking about."
And so on. 
When the actual attack comes, Scout (and by extension, the reader) still cannot really tell what is going on.  
After the attack, as she makes her way back to the house, following the mysterious man who is carrying Jem's body, Scout still does not know what really happened. (It will take the next few chapters for everyone to sort out the logistics of what happened.) When she first returns to the house, her question is, "Is Jem dead?" The adults in the house are just as confused as Scout. Aunt Alexandra is so distracted that she hands Scout her overalls to put on (Aunt Alexandra hates Scout's overalls, and prefers she wear dresses).  
The confusion, and hence the tension of not knowing exactly what happened, continues until the very end of the chapter. People come and go, including the doctor and Heck Tate. When Heck Tate gets there, he takes his time revealing the identity of the man under the tree. This keeps the ominous tone going until the very last line of the chapter.