“Well, I’ll be . . . ,” Grandpa said in wonder. He took the controller Dominic held out to him and set the plane on the table. Everyone cheered when it lifted off.

And after that the party really got started. Grandpa turned on an old Beatles album, and we took turns flying the Thunderbolt. Mr. Petrecelli told Grandpa about his favorite places in Italy, and then—like I’d predicted—they started arguing about the shrubs in the front yard. Mom and Dad did some kind of swing dance in the middle of the room, and Penny and Sarah swapped dance recital stories.

“Well,” Grandpa said, coming to sit down beside me with his second piece of cake. “What did you think of our little Rube Goldberg machine?” He motioned toward the balloons, which were still all over the floor. “Your dad and I put it together. We call it the Party-Matic 2000. I know it’s simple compared to what you’d dream up.” He smiled. “But we’re no bronze medal winners.”

“I love it, Grandpa,” I said, picking up a red balloon and throwing it into the air. And I meant it. It was true that the balloon drop hadn’t been complicated, but that didn’t matter. The best part was that my dad and Grandpa had taken the time to put it together for us. Plus, to tell the truth I was feeling kind of done with complicated Rube Goldberg machines. Lately I’d been more into geology. Did you know that if a supervolcano were to erupt, it could rain hellfire across thousands of miles and cause worldwide climate changes? Crazy, right? Maybe next year I actually will do my science fair project on Mount Saint Helens. It’s pretty fascinating stuff.

“Look at that,” Grandpa said now, glancing down at my empty paper plate. “You need a second piece of cake.”

He went off to get me a big piece with lots of icing, and while he was gone, I picked up another balloon and bapped it at Penny, who bopped it to Dominic, who tried to thwack it back, except he aimed too high and hit the banner, which came loose from the ceiling and fell down on my head.

“Dominic,” I groaned, unsticking the tape that had caught in my hair.

“Sorry,” he yelped, except he didn’t have to apologize. If anything, I should have thanked him, because the way the banner fell suddenly gave me a great idea for improving Grandpa and Dad’s Party-Matic.

What if, instead of just hanging the banner with tape, we strung it up on the old clothesline from the Tomato-Matic? We could also add a small weight to the net full of balloons. When you turned on the light, the string would get pulled, releasing the net—just like before. Except now when the net opened, the weight would also fall. If we attached a string to the weight, it could trigger a simple motor. The motor would start up, and the banner would unfurl across the room. Then, for a dramatic finish, we could rig up a few bags of confetti, which would explode like fireworks when they were pierced by a pin on the end of the unfurling banner. It would be so cool!

Grandpa sat down beside me and handed me my piece of cake. “You looked a million miles away there for a second, Ruby,” he observed. “What were you thinking about?”

Mom laughed as Dad dipped her so low that her head almost touched the floor. Mr. Petrecelli bit his lip as he maneuvered the model plane around a hanging plant, and Penny looked across the room at me and smiled.

“Nothing much,” I said, taking a bite of cake and letting the icing dissolve on my tongue. Maybe the Party-Matic was working fine just the way it was . . . even without exploding bags of confetti. After all, when you had as many good people in your life as I did, you could afford to keep it kind of simple.