The Late Steve Smith (Family Dad)

Plot
Steve and Debbie's growing relationship is marred by Steve's constant tardiness. After arriving late for school and their date because Peter and Francine were having loud sex at their room, Steve is determined to make it up to Debbie by skipping a party hosted by Mayor Adam West and meeting Debbie for a birthday dinner date at "Cavern on the Green," a fancy restaurant situated in a deep cave with naturally occurring stalagmites. As Steve prepares to leave for the date, Stewie forces him to test his newly invented one-way time machine, which is only able to travel to the future (to prevent changing the past and the creation of paradoxes), by moving one minute forward in time. As Stewie, Steve and Brian prepare the machine, Steve records a message in a video birthday card for Debbie, apologizing for being one minute late and explaining the situation. As he is about to finish, Stewie accidentally pulls the lever too far, sending them forward into the year 10,000 AD. During the trip, Steve loses the card in the time stream. Meanwhile, a nuclear accident at Mayor West's party kills all but West, leading Debbie and the Smith family, who think Steve and the others had gone there, to believe the trio are now dead.

Stewie, Brian and Steve decide that their only hope of returning to the 21st century is to continue forward in time until they reach a period in which a time machine that can travel to the past has been invented. However, they are repeatedly sidetracked during their travels, encountering numerous periods of Earth civilization (at one point managing to find a time period populated by beautiful women who have mastered backwards time-travel, but are sent forward by an angered Brian, who was not let off in an era where dogs were conquering humanity), until they arrive at the year One Billion when Earth is barren and all life extinct. Back in the 21st century, THE Smiths have left Quahog out of grief for the apparent deaths of Brian, Stewie and Steve, while Debbie has married with a successful man, but still harbors some nostalgia and hurt toward Steve for standing her up before his "death". In the year 2050, she finds the lost birthday card as it emerges from the time stream and learns that Steve did not mean to abandon her. She goes to the empty Cavern on the Green and fires at the ceiling in a way that results in mineral water dripping to form stalagmites that create a message Steve discovers one billion years later, reading that although their time together was short, it was the best time of her life.

Having lost their opportunity to return home, Steve, Brian and Stewie resign themselves to going to the end of time. After the last existing proton decays, they are amazed to discover that the now empty universe undergoes another Big Bang, and furthermore that it replicates the same universe and its exact events, instead of having unique inhabitants and history. They realize that they can continue forward in time and eventually reach the moment that they left in the new copy of the universe. They succeed after overshooting their first attempt, though the new universe is about 10-feet lower than the previous one, causing the time machine to crush their duplicates in the new universe to death as they enter their machine (avoiding a time travel paradox). Steve rushes to meet Debbie and manages to make it to their date on time. After dinner, Steve apologizes to the family for being late, and for losing his birthday card to Debbie, but Debbie dismisses it and tells him that she will always remember their time together. Stewie can be seen at the Smith's house backyard, burying the bodies of the dead duplicates.