Brian makes a bold move to help sleep with women: he impresses them by taking them into the past to see history unfold. However, after one woman points out that Brian's been causing the odometer on the time machine to increase. In order to hide it, he tries rolling it back himself, but in doing so, he causes time to start flowing backward.
Brian and Stewie, who caught Brian using his time machine, suddenly realize their predicament when they see various events of the show's history happening, but in reverse. Stewie tries to fix the machine but can't figure out how to recreate the shockwave that would correct the flow of time. All the while, the flow of time is accelerating, taking them through Stewie's teething and eventually to his birth. Brian must fix the time machine without Stewie's help. So, in a last-ditch effort, he decides to turn the odometer forward, which creates the exact opposite effect and restores forward time, just as Stewie is being born.