“Have you ever heard of someone called Ishango?” I asked over my shoulder.

“No,” Mom said. “Does he live here?”

“Not that I know of,” I said. “Just heard the name.”

After digging around in our dim, dusty crawl space, I emerged with the “I” book of our encyclopedia set.

“What are you up to?” Mom asked.

“Checking something out,” I said, lying on my stomach on the floor and opening the book in front of me. “Had a research paper idea.”

There it was: Ishango. Part of a national park in the Democratic Republic of the Congo, described as one of the most beautiful places in the world. Home to one of the largest concentrations of hippos in the world. Also the name of a Congolese nature preservation organization.

Another entry followed: Ishango bone. A Stone Age tool made from a baboon bone with markings carved into its side. According to the encyclopedia, it had long been assumed to be a tally stick, but now it was thought to be part of some other type of ancient mathematical tool. One side grouped tally marks to make prime numbers adding up to 60: 19 + 17 + 13 + 11, for instance. The other side’s marks were related to more disputable equations. It wasn’t exactly the theory of relativity, but this might have been the earliest known mathematical system.

What any of this had to do with Mount Hope, I had no clue.

I closed the book and looked up at my mom, who was beaming at me.

“Stop it,” I said.

“Seriously, how many years did that take?” she asked.

“We’re still in friends mode, actually,” I said.

“Huh. Could’ve fooled me.”

“Well,” I said, getting up, “we are going to the homecoming dance together.”

“He finally asked!”

“Vice versa, Mom. I’m a modern woman.”

“So you are.”

“I’ll just search online for a dress. Oh, wait …”

“I’ll dig out my old sewing machine and make you something out of the drapes,” she volunteered.

“Thanks.”

“Hold on a sec.” Mom disappeared into the closet and rummaged around. She was really pretty, even in her jeans and a T-shirt. I could imagine her going to a dance when she was younger—or now, for that matter. She was far from ancient, having had me when she was nineteen.

“It’s a couple years old,” she said as she reemerged, “but I hung on to it in case someone asked you out when you were a freshman.”

She handed me a Nordstrom’s prom catalog. On the cover were three girls who were hyper-skinny and showing way too much … everything.

“Perfect,” I said. “Now if only there were a Nordstrom’s on this side of the roadblock.”

“You look at it for ideas,” she said.

I opened onto a page showing a lacy thing that resembled lingerie more than a dress. “That’s a no.”

But as I stared at the revealing gowns, I got an idea.

“I think my arms are too weird for dresses like this,” I said, rolling up my T-shirt sleeves to expose my bare shoulders.