“Just because you don’t have a sense of humor,” Theo said.

They climbed the steps to the third floor and approached the information desk. The librarian was a youngish woman with short black hair, tan skin, and huge green glasses that swallowed most of her face.

“Sure, you’ll find plenty of material under the heading ‘Sioux,’” she was saying to the teenager in front of her, “but the word Sioux is a colonial word, a mispronunciation. I would also look up the Lakota and Dakota.”

The teenager, a white kid wearing a wool hat that made Theo itch just looking at it, said, “Why are there so many different names for the same people?”

The librarian shrugged with one shoulder. “What other people call you is not always what you call yourself. Sometimes it’s out of disrespect. Sometimes it’s out of misunderstanding.”

“Huh,” said the kid. “Never thought of that. Thanks for the info.”

“Happy to help,” said the librarian.

The kid tipped his woolen hat and turned to leave. His eyes widened at the sight of Nine, but then he tipped his woolen hat at her, too, before walking away. The librarian waved Theo, Tess, and Jaime forward.

Jaime said, “Hi! We’re here to see some letters in the Pforzheimer Collection?”

“Ah! Fabulous! Which letters would you like to see?” the librarian asked.

“The letters from Ada King to Charles Babbage?”

“The Countess of Lovelace! Isn’t that perfect title for a mathematician? Countess? Get it?” said the librarian.

“You have an excellent sense of humor,” Theo announced, mostly for Tess’s benefit.

“That’s very true, though not everyone appreciates it,” said the librarian.

“Tell me about it,” said Theo. “I mean, you don’t have to tell me about it because I know. Uh, unless you want to.” Tess and Jaime turned to stare at him. Theo’s face got hot, as if he were outside in the humid air instead of inside of the library.

The librarian didn’t seem to notice his awkwardness or had so much experience with awkwardness that his wasn’t remarkable.

Theo liked her eyeglasses.

“There are some procedures you have to follow if you want to see the letters,” she told them. “You can’t take them out of their sleeves. And you can’t take them out of the library. And I’m sorry, I know your kitty is a therapy animal, but fur doesn’t always agree with old documents. I’d like her to stay out here with me, if that’s okay with you. And her.”

Nine peered up at the librarian and meowed.

“That’s okay with her,” said Tess.

“Great,” said the librarian, whose name tag said Dr. Deborah Little Crow. “I’ll show you to room 319 and retrieve the letters for you.”