When Stewie uses his time machine to embarrass Brian in the past, an accident lands the 2 outside the space time continuum.
The only way to return to reality is to explode the return pad. Once safely home, Stewie discovers his return pad explosion was the origin of the universe.

While trying to find plutonium to build another return pad, Bertram discovers Stewie has a time machine and hatches a plan to destroy one of Stewie's ancestors without realizing Stewie's destruction means the end of all existence.