Amp sat on the alarm clock I kept next to my bed. My mom was waiting downstairs to drive me to school. The time on the clock told me I had missed the bus fifteen minutes ago and would probably be late for school. I also hadn’t finished my homework, and I didn’t have an experiment for the science fair yet. So really, being late was the least of my worries.

“Listen, Amp, I have a D in science right now,” I said with as much patience as I could muster. “Miss Martin told us—”

“What’s the D stand for?” he interrupted.

“It stands for . . . ,” I began, trying to remember what the D stood for. “I can’t remember! The D stands for disaster, okay! Or dummy! Or dimwit! It doesn’t matter what it stand for. It’s bad!”

“If it stands for bad, it should be a B, not a D,” he said.

“No, a B is good,” I said.

“Good should be a G then, right?”

“Gosh dang it, Amp!” I howled. “You can’t change the grading system that’s been around since my parents were kids. You’re missing the main point.”

“Hey, I have a great idea for a science experiment.”

“Oh, yeah?” I said nervously. A great science fair experiment would definitely help my grade. “What?”

“I’d need some special equipment, of course, and I’d need to sequence a sample of your DNA, but growing a third arm would be really interesting, and easier than you think.”

I stared at him. He was either clueless or intentionally trying to make me angry. I could never tell which. “I can’t grow another arm!” I shouted. “None of my shirts would fit.”

“But you’d be a heck of a juggler,” he said softly.

“I can put you in a hamster cage, you know,” I said.

“Okay,” he said, holding up both hands in surrender. “I’m just asking that you think about it.”

I grabbed my head and squeezed it, which, surprisingly, helped me remember something. I jumped up and pulled my science textbook out of my backpack and flipped through the pages. There were twenty or so suggestions for classroom experiments in the glossary in the back. One caught my eye. It showed a potato with a bunch of wires stuck in it and a small lightbulb that was lit up next to it. It was labeled POTATO BATTERY. All I’d need was a potato, some wires, and a lightbulb. How hard could that be?

“Easy,” I announced. “I’m going to make a battery out of a potato.”

I dropped the book on my bed and pointed to the two photos.

Amp leaped onto the bed and stepped onto the open page. He read in silence. Studied the photos for a minute, stroking his tiny blue chin the whole time.

“Seems kind of dull,” he said.

“No, it seems easy. A simple potato battery is perfect.”

“Whoa, someone didn’t brush his teeth this morning,” Amp said, waving his hand in front of his face.

“Funny,” I said. “That’s what I’m making.”

“Fine, but I should warn you that—”

Just then my door popped open and my mom stuck her head in.

I whipped my head in Amp’s direction.

But Amp was gone. I looked around, but, thankfully, he had vanished. Mom hadn’t noticed. He really was the fastest thing I had ever seen—or not seen.

“Who on earth are you talking to up here?”

“I’m . . . . I’m practicing my science fair presentation,” I said weakly.

“You’re still doing your homework, Zack?” She sighed. “C’mon, I need to get to work. Better fix that hair first, honey.” She headed back down the hallway.

“One second, Mom,” I called after her.

“Between her popping in all the time and your brother snooping around, I’m getting nervous about being discovered.”

I froze. “What? Taylor’s been in here? Looking around? Has he seen you?”

“No, because I usually make myself invisible. Would you like me to tell you how?”

“No, I don’t care how. We just can’t get caught. If someone sees you they’ll take you away, Amp. Then you’ll never get home.”

Amp looked concerned. “One of these days our luck will run out, Zack. I think your brother is suspicious. We need to get my spaceship repaired!”

“We will, Amp. As soon as I get through this science fair. I can only handle one disaster at a time.”