Henrietta was ten, almost eleven, that spring of 1863: sturdy and energetic, tall for her age, with her dark hair still hanging in two long plaits. An excellent speller with a tidy, legible hand and a curiosity that offended some of her neighbors, but not, fortunately, her new employers. Henrietta knew, because she asked, that the letter writers were Mr. Deverell’s younger brothers Izzy and Vic, who were twenty-three and twenty-one, and that they’d enlisted in part because of the bounty. But what was a bounty? (Mrs. Deverell, who asked Henrietta to call her Aurie, explained.) And why were Vic’s letters so short, while Izzy’s went on and on? (“Brothers,” Mr. Deverell said with a shrug.) She preferred Izzy’s letters, both sides of five or six sheets filled with gossipy details, late additions and afterthoughts winding up the margins until he ran out of room entirely. But what was a company, what was a regiment, was a corps larger or smaller than a brigade?

“Larger,” Mr. Deverell said. (He hadn’t asked her to call him Maurice.) A corps was made up of several divisions, a division made of several brigades; a brigade contained four or five regiments, and a regiment like Vic and Izzy’s began with ten companies of roughly a hundred men each but shrank as men got sick, deserted, were wounded, were—he stopped there, he would not say killed. She was taking notes.

“That,” he said, as she sketched a nested set of boxes in boxes, “is enough of that. Now go help Aurie.”

After the first week, Aurie gave her a pencil and let her number the pages and, if the letters were dated vaguely or sited anecdotally—Next day, early morning. On a log, at camp 1 mi from white church—add a tentative calendar date and location. From the newspaper Henrietta had cut out woodcuts of the camps and the hospitals. From a magazine, a map of northern Virginia showing the rivers and towns. No one minded if she read the earlier letters and tried to match newspaper accounts of events with what the letters reported, as long as she kept a close eye on Bernard.