(Maybe you’re starting to wonder why Lulu’s mom and Lulu’s dad would ever hire someone who would wear a menacing uniform and combat boots. All I can tell you is, first, everyone said that Ms. Solinsky was the best babysitter in town—maybe the world—and, second, she may not have looked like that when they interviewed her.)

But she sure looked like that now, and, as I already pointed out, anyone else would have shivered and said, “I surrender.”

Not Lulu.

Indeed, when Ms. Solinsky reached her hand out for a handshake, Lulu, instead of politely reaching back, crossed her arms across her chest and tucked her hands emphatically into her armpits. “Maybe you can’t catch something from me, but I,” said Lulu, “might catch something from you. And maybe what I might catch could make me even sicker than I already am.”

“Well, aren’t you the sensible one!” Ms. Solinsky exclaimed. “But still—no problem.” She dug into her duffel bag, pulled out a packet of disinfectant wipes, and briskly wiped down her hands—first left, then right. “I’ve just killed off my germs, which means you can’t catch something from me,” she said to Lulu. “So now”—she reached out again—“shall we shake hands?”

Although there was a question mark at the end of this last sentence, this wasn’t a question.

Lulu shook hands.

After the handshake Ms. Solinsky told Lulu’s mom and her dad that if they wanted to pack for their trip, she would stay with Lulu and keep her company. “We’ll do just fine,” she assured them as they gratefully rushed from the room, moving so fast that they didn’t see Lulu frantically shaking her head and mouthing (so Ms. Solinsky wouldn’t hear her), “Don’t go.”

The minute they were gone Ms. Solinsky brought her unsmiling face down close to Lulu’s and said, “That I’m-so-sick routine may work out great in a storybook or in a movie, but don’t waste my time trying it on me. You’re in excellent health, and I want you on your feet, in your shoes, standing tall, arms straight down at your sides in exactly”—she looked at her wristwatch—“ninety seconds.”

No grown-up in Lulu’s entire life had ever dared to talk to her that way. And no grown-up, Lulu decided, would be allowed to. And so, without saying a word, she pulled the comforter over her head and pressed her body hard into the mattress. She could hear Ms. Solinsky counting down—“eighty seconds . . . sixty seconds . . . thirty-five . . . twenty-five . . . fifteen seconds . . . time’s up.” And then, without taking a breath, Ms. Solinsky swooped an astonished Lulu out of her bed, set her onto her feet and into her shoes, pushed back her shoulders, lifted her chin, and pressed a firm palm against her droopy spine.

And—what do you know!—there was Lulu, standing tall, head high, her arms straight down at her sides. Looking good. But not quite good enough.

“Hmm,” muttered Ms. Solinsky as she walked around her, carefully checking her out, “I see we have a lot of work to do.”