As the crew are travelling as usual, a new Rimmer appears from an alternate universe, Ace Rimmer, who is dashing, handsome, charming and heroic - making the Rimmer aboard Red Dwarf sicker than ever before.
An a Rimmer from an alternative universe, known to his friends as Ace, test pilots an experimental spacecraft for the alternative Space Corps. He arrives in our universe, where he crashes into Starbug, which is forced to land on the surface of a desolate water planet. Ace, seeing their predicament, comes to their rescue.
After repairing the ship, the two Rimmers take an instant disliking to each other, with Arnold implying Ace is gay. However, the rest of the Boys from the Dwarf take a liking to Ace, mainly because he possesses few of the annoying qualities of Arnold Rimmer.
However, Ace doesn't stay much longer. He decides to leave after finding Arnold too boring and unbearable to live with. Before he goes, however, he reveals that the point at which Arnold's and Ace's lives separated was where Ace was kept down a year in school while Arnold went up. This explains his determination to succeed, and that Rimmer had it easy so he never had to learn any of the skills that made Ace different.
On Io, a young Arnold Rimmer has been tied upside-down to a tree by his brothers. His unconcerned mother explains to him that he is in danger of being held back a year at school, which could affect his whole future...
Twenty years later, Arnold "Ace" Rimmer is a Space Corps test pilot on Mimas. He is a very popular and confident man who is at the top of his profession, so when he is offered the chance to test a new ship that can cross dimensions, he jumps at the chance to meet another Arnold Rimmer. He leaves his friends Spanners, The Padre, Mellie and Bongo behind, knowing that he will never be able to return. He parts from them with his catchphrase "Smoke me a kipper, I'll be back for breakfast".
Aboard Red Dwarf, Lister, Kryten, The Cat and even Holly try to leave Rimmer behind while they go on a fishing holiday to an ocean moon. Rimmer catches them and insists on coming along. When Starbug encounters Ace's ship bursting through into their reality, they adopt the crash procedure which involves reading the incredibly boring in-flight magazines. They manage to survive hitting the Wildfire, but crash onto the moon's surface.
The Cat is badly wounded, caring more about the blood clashing with his trousers than with the injury. Lister decides to try fixing the damaged engine before Starbug sinks, but he knows little about it. Ace arrives and immediately takes charge, charming everyone and insisting that Rimmer will be able to help. Rimmer proves ineffective and cowardly, so Lister joins Ace in fixing the engine.
Rimmer soon learns to resent Ace's presence. Ace is a reminder that with the right breaks, Rimmer could have made a success of his life. After Ace repairs The Cat's broken leg, Ace tells Lister that the only difference between his life and Rimmer's was that Ace was the one who was held back a year in school. The humiliation made Ace buckle down, forced him to fight back, and helped him later develop confidence and concentrate on being a better person. So ironically, it was actually getting a break for once that caused Rimmer to grow up into what he is.
Ace decides to leave Red Dwarf, going off to explore other dimensions partly because he cannot stand to be near his counterpart. Rimmer decides to teach him a lesson, rigging up a net full of kippers to drop on Ace's head. The net does not work and Ace flies off to new adventures, searching for a Rimmer as sad and worthless as the one on Red Dwarf...his impossible search continues.
As available for viewing on the Series IV DVD:
- Extended model shots of Rimmer's childhood home on Io, including the Rimmer house which was not seen in the episode. Only a wider shot of the whole colony, and the gardens of the Rimmer family home, are seen in the episode. However in the model shots on the DVD the house can be seen - which was seemingly very modular, and resembling grain silos.
- Ace Rimmer's scene with Padre was originally longer, talking about how Ace had helped little orphan boy Tommy pull through after an operation. The extended dialogue also says that Ace donated all his money to helping the boy.
- Mellie also had an extended scene, asking Ace to bring cherries as well as maple syrup to their tryst, and breaking the fourth wall to say "what a guy".
- Blue-screen work was not completed on Ace's farewell scene on Mimas, which continued a running gag as Padre smells maple syrup on Mellie, and also includes Bongo and Spanners musing on how Ace will encounter another Arnold Rimmer and become fantastic friends and an exceptional team with his counterpart.
- A half dozen additional lines of dialogue and jokes, cut for time.
- The original ending to the episode whereby Rimmer with the help of the skutters tries to drop a sack of kippers on Ace, but they fall on him instead, was removed when the writers believed it didn't work on either comedic or logical levels. The kippers, which should have fallen straight through the hologram Rimmer, were intended to halt in freeze-frame. In the aired episode, Ace merely shrugs at the still-suspended kippers before walking off.
- For the last two episodes of Series IV the closing credits do not include the standard Red Dwarf theme song. At the end of Dimension Jump, the theme song is played by Rimmer and the Skutters on the Hammond Organ without any lyrics. In Meltdown, the Elvis look-alike waxdroid sings the Red Dwarf theme at the end.
- Dimension Jump is the last time that the Skutters are seen until the Series VIII episode "Back in the Red Part II" (Lister refers to two of them as Bob and Madge) since the Boys from the Dwarf are without Red Dwarf for two series.
- This is the first appearance of Rimmer's heroic alter ego Ace Rimmer.
- The Series VII episode "Stoke Me a Clipper" is a sequel to this this one in more ways than one. The Ace Rimmer in "Dimension Jump" says that he has "billions" of other Arnold Rimmers to meet, which foreshadows the events of "Stoke Me a Clipper" where it is revealed that there have already been billions of Ace Rimmers saving the Universe, one passing on the flame to another..
- When we see young Arnold Rimmer hanging upside-down from a tree in the family garden on Io at the beginning of this episode, the gardens were presumably the work of Dungo aka Dennis the Gardener. Not to mention, given his mother showed very little interest, it might well have been Dungo who untied him. In the final episode of Series X, it is revealed that Dungo was actually Arnold's biological father, making this more likely.
- Rimmer: I went into the gents and he went the other way (About Ace)
- Ace Rimmer: Smoke me a kipper, I'll be back for breakfast.
- Spanners (Alternate Lister): What a Guy!
- Padre (Alternate Cat): What a Guy!
- Bongo (Alternate Kryten): What a Guy!
- Hatty Hayridge's "alternate dimension" character also got to say "What a guy!" but this was cut from the final broadcast, possibly due to the fact she's the only one of the characters to break the fourth wall when she says it. A second reference to the maple syrup gag was also cut.
- Possibly unintentionally, Robert Llewellyn's alternate dimension character Bongo bears a striking resemblance to Dean Stockwell's character Al Calavicci of Quantum Leap fame. (Al's character in Quantum Leap was nicknamed Bingo ''in his youth (A Leap for Lisa) which was a shortened form of Bingo, Bango, Bongo)
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