In the nineteenth century, the accepted scientific theory was that lightning produced a vacuum. A vacuum is a space devoid of matter. A vacuum could theoretically be related to a wormhole.

That last fact is how I found a whole subthread of comments from people—people who I am going to assume are scientists—talking about how the likelihood of finding a wormhole is increased during a thunderstorm. This is because of the energy created by thunderstorms, and energy is what helps bring out “exotic matter.” And “exotic matter” is what makes wormholes appear.

“Bingo,” I say over and over again as I read through the thread. Mabel used to make fun of me for saying that. She said it made me sound like an old lady, which is fair. I probably picked it up from Grams.

Out of the corner of my eye, I see Mabel’s empty bed. “Bingo,” I repeat, looking at it for so long without blinking that my eyes begin to water.

I can’t wait to say “bingo” to her again. I can’t wait to tell her that it was a quote from our mom that helped me solve the mystery of how to bring her back. I absolutely can’t wait.

I pull up the weather report for this week. Meteorology is, of course, not a precise science, but for this particular experiment I am going to have to rely on it.

I’m staring at the thunderstorm icon hovering over today’s date, when there’s a knock on my door.

“Cora?” Grams opens the door without asking. The knock was my warning. That’s how it works with Grams.

I push my wheelie chair away from my computer to face her. “Huh?”

Grams’s eyes narrow with concern as she takes me in. I admittedly do look pretty rough. It’s late in the afternoon and I’m still wearing my pajamas. My eyes are red from staring at the computer screen for hours on end, and my pajamas are covered with crumbs from the granola bar I ate for lunch.

“Cora London,” Grams says. “What project are you working on now?”

I wince as she turns on the light. I’ve been working in the dark. Something about the glow of the computer helps me concentrate.

“It’s nothing.”

Grams makes a disbelieving clicking sound with her tongue. “It doesn’t look like nothing. It looks like it’s running you ragged. Have you eaten anything of substance all day?”

Before I can answer, Dad walks into the room. He looks a little bit rough, too. His pants are wrinkled and he has ink splotches on his hands. It must be a grading weekend.

“You don’t look ready for the fall festival,” Dad says. It’s then that I notice he’s holding a camera. And not the type that comes with your phone, but the real deal.

“What?”

“Grams called me in here to see you off to the festival,” Dad says.

“It’s the fall festival tonight. A Chestnut Middle School tradition,” Grams says.

“Um, I know what it is.” I cross my arms over my chest. I look down at my crumb-covered pajamas. “But I’m clearly not going.”