Number 2 was working very late in his laboratory as always. He was trying to create a super hamster and now he was ready to make some tests. He placed a hamster under his machine and turned it on, however the frightened animal ran off and he ran after him. That caused he's hit by his own device and started to stretch.
Meanwhile, his friends were watching television until a weary teenager walks in, it was Number 2 who had grown up at least 6 years older, with lanky limbs and big hands and feet. Luckily for him, his clothes grew up with him somehow, but his friends still didn't recognize him and threw him out of their treehouse.
Number 2 was writhing in pain when a girl ran over his stomach by accident with her bike and falls over. When she confronted him, they suddenly and seemingly fall in love at first sight. He got up and nervously asked if she would like to join him on a date, to which she agreed. They had their date but randomly his age transformation started to reverse and he constantly needed to go back to his room to turn himself into a teenager again.
After several uses, the machine started to break down, and when the hamster tried to use it. The ray malfunctioned and the power went out in the whole treehouse. When number 2 and the girl were about to kiss, she got a call on her cellphone and suddenly cut the date short. Before leaving, she gives him a kiss and unexpectedly invented him to join her to where she is going, to which he agreed.
Meanwhile, number 2's friend were interrogating the hamster about the energy problem and number 2's disappearance when a weird ship crashed into the treehouse shooting lasers. Inside there was number 2 and the girl who immediately began to fight number 2's friends. She was easily winning until number 5, her little sister, appeared and disarmed her. Then, they began to fight, but the older sister was stronger.
However, when number 5 was going to be defeated, the older sister was suddenly captured by number 2, before he revealed his true identity by turning back into a kid.
Later on, two other kids shown up and arrested the girl and took her to a prison while a third one made a report about what happened. When he heard about number 2's age machine, he got worried and used a device to read the radioactivity in the room. It was too high that he closed the area. And ordered number 2 and his friends to stay away from there. He needed to go back to the moon base and prepare a way to clean that place before a catastrophe occurs.
A few minutes after the kids left the treehouse, number 2 started to shine like when he was hit by the age ray and suddenly turned into a teenager again. He can't understand how it was possible. He didn't use the machine and now it was broken. Number 1 knew that if the other kids discover this, number 2 would be expelled, so he ordered number 3 and 5 to go to the moon base. They will offer their help but the real purpose was to distract and prolong their return until number 2 becomes a kid again.
With number 3 and 5 going to the moon base, the treehouse was now inhabited only by the boys and since number 2's room was closed, Number 1 ordered him to sleep with number 4. He said they will think of what to do in the morning and left. Number 2 awkwardly stared at number 4 who didn't seemed pleased with the idea of sleeping with a teenager, even if he actually was his best friend.