In the distant future, Rigby, Benson, Skips, Hi-Five Ghost, Muscle Man, and Pops fight Lord Ross, a
madman plotting to erase the timeline. Aiding him is a cybernetic Mordecai who is estranged from Rigby for a past transgression. The entire team is killed except for Rigby, who escapes using a timeship, a
time traveling
space vehicle, to travel to the past, though not before Mordecai mortally shoots him. In the present, Mordecai and Rigby barely convince Benson not to fire them after running late due to Rigby's idea to get
breakfast burritos. Future Rigby then crashlands in the park, saying that when Mordecai and Rigby were in high school, they built a time machine that backfired and created a "Time-nado", a
tornado able to travel through space and time, which was later harnessed and weaponized by their former science teacher and volleyball coach, Mr. Ross, who was held responsible for the incident and arrested. Before dying, future Rigby tells his present self that he will soon have to reveal a secret from his past to save the universe, even if it destroys his friendship with Mordecai. Mordecai explains they created the time machine because Rigby got into their dream college, College University, but he did not. After preparing for the mission, the employees use the timeship to travel back in time, damaging the engines in the process. Skips, Muscle Man, and Hi-Five Ghost stay behind to fix them, while the others go to Mordecai and Rigby's old high school to destroy the time machine that their past selves are working on. Mr. Ross is angry at Rigby for costing his volleyball team the championship but is forced to let him do an
extra credit assignment to pass his class. After an encounter with the volleyball team, who mistake Benson and Pops for spies from a rival school, Mordecai and Rigby meet their past selves and convince past Rigby to make a model
volcano instead, before destroying the time machine. Believing their mission to be over, Mordecai, Rigby, Benson and Pops return to the timeship. but after it is repaired, temporal ruptures begin appearing; it turns out that Rigby and Mordecai's past selves are about to finish a second time machine Lord Ross planted. The employees race back to the school but are held up by Lord Ross and future Mordecai, allowing past Mordecai and Rigby to botch the second time machine and create the Time-nado. Lord Ross then forces Rigby to admit the truth: he never got into College University, but Mordecai did. Unwilling to get separated from Mordecai, he created his fake rejection letter to maintain their friendship. Lord Ross then tries to kill Mordecai with a volleyball bomb. However, Future Mordecai, having a change of heart, jumps into the bomb's path, forcing Lord Ross to retreat. Enraged at Rigby's duplicity, Mordecai ends his friendship with him. Heartbroken, Rigby runs off with the timeship, leaving the group behind. Before dying, future Mordecai gives his present self his timeship and advises him to patch things up, expressing regret over the corrupt path he chose. As the group tries to rebound, a distress call from future Gene the Vending Machine prompts them to help out. After a
suicide attempt by flying into the
sun, Rigby encounters Father Time, who is falling apart due to the Time-nado. He convinces Rigby to head to the future and apologize to Mordecai. At the Time-nado
space station, Lord Ross intercepts Rigby and Mordecai. With Techmo's help, they defeat Ross and restore their friendship before using the
plutonium from Mordecai's timeship to destroy the Time-nado, later convincing past Rigby to apologize to past Mr. Ross before the latter is arrested, ending the feud between them. Returning to the present, Mordecai and Rigby agree to not let their friendship degrade into trying to kill each other, altering the future and erasing their dead future selves. The next day, as Benson catches them out of the park, the pair race back in the timeship from a fast food place, glad that they will "never be late again". ==Cast==