The parents went to the hospital and gave the wrong information to the nurse. At delivery the doctor hit the baby out the window. Meanwhile a bad guy drained Captain Underpants' power and gave some to a dog. The rest of the formula is what the baby landed in. The bad guy insulted the baby and the baby beat him up. Then the police came and saw this situation. The bad guy went to jail. The nurse discovered the baby but the baby flew to his parents carrying the nurse. Then Super Diaper Baby picked up the doctor and spanked him. Then the mom and dad who named him Super Diaper Baby. The evil guy gave the parents a crib that will drain the baby's power. However, the baby needed changing and mom left the diaper full of poo in the crib and when the evil guy drained the power, he only drained poop. So on his way to make a new plan he got stepped on and put in the trash. He vowed revenge. He then built a machine insect he controlled from the inside to destroy Super Diaper Baby. Super Diaper Baby almost destroyed it until the insect grabbed him to drop the baby in a volcano but the dog saved him. The dog pushed the insect into the volcano. The evil poop got didn't die he only got bigger and meaner. He started stomping around. Diaper baby grabbed a giant toilet paper roll and wrapped the poo and took it to Mars. The baby and dog to a bar while they were in outer space. They bought a super power drink and gave it to Captain Underpants. Captain Underpants regained his strength. The baby and dog went home. The dog got a diaper too and he and the baby was matching. Everyone was happy. The end.