Jem's hit the middle school years, and everyone knows what that means: he's angsty, moody, prone to prolonged silences broken by angry outbursts, and he all of a sudden thinks Scout should act like a girl.
Scout asks Atticus and Calpurnia what's up with Jem and whether she can fix it by beating him up, but they say he's just growing up and she should leave him alone.
To make things worse, Dill isn't coming for the summer.
And then to make things the absolute worst, Atticus (who's a member of the state legislature) gets called into a special session and is away for two weeks.
With Atticus away, Calpurnia doesn't trust Jem and Scout to go to church by themselves (there was a past incident involving tying up one of their Sunday School classmates in the furnace room), and decides to take them with her to her church instead.
On Saturday night, Cal scrubs Scout down to her bare skin and makes sure that there's not a thread out of place on the kids' clothes.
Why? As she says, "I don't want anybody sayin' I don't look after my children" (12.31).
On Sunday, they head over to First Purchase African M.E. Church outside of town.
Everyone's happy to see them, except one: a tall woman named Lula who asks Calpurnia why she's brought white children to the African-American church.
For a minute, things look like they might get ugly, but then the crowd drives Lula off and welcomes the kids.
The church is plain and there aren't any hymn-books, but Cal won't let Scout ask questions.
The priest, Reverend Sykes, begins the service by welcoming the Finches, and then reads some announcements.
One of the announcements is that the day's collection will go to Helen, Tom Robinson's wife.
Zeebo leads the congregation in a hymn by reading out each line of the lyrics, which everyone else sings after him, surprising both Scout and Jem, who had never heard of such a thing before.
Reverend Sykes gives a sermon, which like that of the Finches' usual preacher, focuses on "the Impurity of Women" (12.79).
Contrary to the Finches' usual church experience, the Reverend names names as to who's been sinning lately, and tells them individually to cut it out.
After the collection, Jem and Scout are again surprised when Reverend Sykes counts the collection money in front of everyone and then announces they don't have enough—they need at least ten dollars to get Helen and her family through the week.
The Reverend goes so far as to lock the doors and hold the congregation hostage until they cough up enough cash.
Jem and Scout put in their dimes from Atticus.
Once the ten dollars is finally collected, the doors are opened and the service is over.
Afterwards, Scout asks Calpurnia why Helen can't find work. She says that Tom's family is being shunned because of his alleged crime.
So, what'd he do? Cal reluctantly tells her that Bob Ewell has accused him of raping Ewell's daughter.
First, Scout wonders why anyone would listen to the Ewells, and then asks Calpurnia what rape is.
Uh, ask Atticus, Cal says.
Now it's Jem's turn to ask questions. Why does the congregation sings their hymns the way they do, instead of saving up for hymn-books?
Well, hymn-books wouldn't do them much good—hardly any people in the church can read.
Cal only can because Miss Maudie's aunt, Miss Buford, taught her to read.
Some other facts about Cal, which Jem and Scout only now think to ask her:
She's older than Atticus though she doesn't know her age exactly, or even her birthday—she just celebrates it on Christmas to make it easy to remember.
She grew up near Finch's Landing, and moved to Maycomb with Atticus when he married.
She taught her oldest son Zeebo to read, too (but not using anything like "This is Spot. See Spot run.").
Nope, she brought out the big guns: the Bible and a book Miss Buford used to teach her—Blackstone's Commentaries, a gift from the Finch kids' grandfather.
Jem's blow away that she learned and taught English out of such a difficult book as the Commentaries. That must be why she doesn't talk like the other African-Americans he knows.
Scout is blown away to think that Calpurnia has a whole other life besides being their cook, much like a child realizing that teachers don't sleep at school.
One last question. Why does Cal talk differently at the African-American church than she does with white people? She says that it makes more sense to fit in.
Okay, this is actually the last question: can Scout visit Calpurnia at her home some time? Sure.
And then they arrive home to find Aunt Alexandra installed on their front porch.