Hacking, Ms. Solinsky explained, was sneaking into other people’s computers—computers sending out messages (like Lulu asking Mabel to bring over cats, or bad guys plotting how to destroy the world) that you definitely weren’t ever supposed to read. Codes were ways of writing your top-secret messages so secretly that, even when hackers read what you had written, they couldn’t understand a single word.

Working with Lulu on Wednesday, Ms. Solinsky first taught her several nifty codes and then moved on to the tricks of hacking computers, solemnly explaining to her, “Hacking is wrong and not nice and against the law, but you need to learn how to do it to be a good spy.”

“And I do want to be a good spy. I do!” said Lulu—and then she dug in and learned how to hack faster than she had learned anything else in her life.

“You’ve got a natural talent,” Ms. Solinsky said to Lulu. “But don’t use it except when you’re an official spy. Because if you’re hacking to find out if Henry likes you better than he likes Nora Kaplan, you probably won’t appreciate the answer.”

“I have no idea what you’re talking about,” Lulu told Ms. Solinsky, who patted her on her shoulder and replied, “You are so much better at hacking than at lying.”