As Derrick returned to his normal size, Tanner was about to make the next change with the Chronivac. However, the doorbell rang and Tanner immediately left his room to answer the door. It was his girlfriend Sarah, who he thought was out of town for the weekend. She wanted to go out (just the two of them), but Tanner wasn't able to since he was stuck with Derrick for the weekend and couldn't leave the house. The two decided to stay at Tanner's for a few hours as Sarah had to work the next morning, but not before Tanner had to force Derrick to stay in his room. Derrick did not take it too well and there was a bit of arguing, but not loud enough for Sarah to hear. Derrick did mention that Tanner owed him for the shrinking, but Tanner got his way in the end. Derrick's grounding was the reason, but he just saw it as an excuse for Tanner to get some alone time. This was somewhat typical for the two, but this time, Derrick was tired of being on the short end just because he's the youngest; he wanted to be the older child for a change. That was when a thought crossed his mind.
As the night progressed, Derrick attempted to sneak into Tanner's room, which proved to be easier than expected since the door was unlocked. Derrick snickered at the fact that Tanner always left the door unlocked despite the knob having a lock. He wanted to use the Chronivac to get some revenge, but not right now. Instead, he grabbed the remote that was next to Tanner's laptop, which had all of the data for both brothers from the scan earlier. Just as he was about to set up the change, he heard Tanner & Sarah head upstairs. Without hesitation, Derrick headed to his room before anyone could see him. While waiting in his room, Derrick set up the changes to the Chronivac. He wanted to switch ages with Tanner, which would make Tanner 8 and Derrick 17. He didn't want to change reality until he was sure that he wants to stay older. He set the change time to be 8 hours long so that they would take place while the two are asleep. Derrick nearly pressed the "Change" button on the remote by accident, but didn't. Later that night, Sarah left the house and Tanner told Derrick that it was time for bed. While Tanner was having his shower, Derrick snuck into his room one last time to steal some of Tanner's clothes in case they would fit him in the morning. Derrick waited another 10 minutes for Tanner to go to bed before pressing the "Change" button and falling asleep himself.
During the night, Derrick was gradually growing into his bed and his pajamas. His pajamas soon started to feel tight on him. He did wake up at one point during the night, but that was because his pajamas were about to rip. As he took them off, Derrick could tell that he already started puberty despite the remote saying that he was only 12 now based on his larger member and his growth spurt since he was last awake. He went back to bed completely naked with his feet just touching the end of the bed. As the night went on, Derrick progressed into his teens with his bed being way too small for him now. While Derrick went through puberty in his sleep, Tanner went through it in reverse as he shrunk in his clothes. Unlike Derrick, Tanner did not notice that he was shrinking, even as his feet were dangling in his clothes or as his stubble was fading.
Derrick was the first to wake up the following morning, not as his normal self, but much older. As expected, Derrick was now Tanner's age, although he was more muscular and taller than Tanner was. Before he could marvel at his changes, he had to show this to Tanner, who was now his old age. Tanner had always found his clothes to be a bit baggy on him, but Tanner's clothes fit Derrick much better. Tanner woke up not long after and noticed that the room was a lot bigger now. "Very funny Derrick." Tanner whispered before realizing how high his voice was. He removed the covers only to find that his clothes are way too big for him. To make matters worse, his member looked way too small to be his. "What the hell?! I'm a kid again!" Tanner said to himself, "But how could this happen? How did this happen?!" Tanner was about to get the Chronivac to get this sorted out, but then he heard a knock on the door. Tanner didn't answer. There was another knock and again, Tanner didn't answer. "It doesn't matter if I see you naked Tanner," Derrick said on the other side of the door, "We're all family." Tanner reluctantly opened to the door to find that Derrick was now towering over him. At first, Tanner didn't recognize him, but based on the behaviour, he was convinced that it was Derrick. "Looks like you ended up even smaller than I was when I was your age," Derrick told Tanner. Derrick then had to explain everything he did the previous night that lead to the two switching ages. Tanner then headed for the Chronivac, only for Derrick to carry him out of the room. "I believe this is my room now big bro," Derrick told Tanner as he carried him to his old room, "And this room is yours." "Okay Derrick. You had your fun, now turn us back!" Tanner demanded, although it sounded more like a childish tantrum. "I'm afraid I can't do that," Derrick replied, "Last time I checked, I'm the older brother now and I say that we stay like this." Tanner was about to close the door when Derrick stopped it from closing. "I believe that shirt is mine now" Derrick told Tanner. Subjecting to his current status, Tanner took the shirt off before throwing it at Derrick and flipping him off. "You know Tanner," Derrick told him, "I don't have to change us back after the weekend. Besides, you're small enough for a spanking now."
With his door locked, Derrick, now in Tanner's old room, looked at the Chronivac to see what he wanted to change next. Alternatively, he could spend a few days as the older sibling.