During a slow day on Red Dwarf, the Cat uses the Dream Recorder to try and look for a dream he once had of four girls and banana yoghurt (at one point, coming across a music video). Rimmer chides the Cat for his views on sex (which involve finding the right "seven or eight girls"). Lister points out Rimmer's own sexist views on women. Rimmer tries to explain his method of meeting women to Lister. Most of his methods involve hypnosis or stupid pick up lines and most attempts end in failure. As the conversation drones on, Holly claims to have invented a faster than light device which he calls the "Holly Hop Drive". The Drive turns out to be a red box with a stop and start button on it. Rimmer scoffs at how pathetic it looks, while Lister is willing to give it a go. After a somewhat worrying countdown, where Holly has forgotten the number seven, they set off for Earth, but they fail. However, instead of transporting them to Earth, it brings them to a parallel universe. In this particular universe, women are the dominant sex, with men being the suppressed gender, and its history is opposite to the Dwarfer's universe, with major historical figures having a male or female counterpart.
Each of the male Dwarf crew has a female analogue. Holly quickly meets a younger, female version of himself, Hilly, and the two flirt. Lister and Rimmer's counterparts (Deb Lister and Arlene Rimmer) have the same personality as their male counterparts. The Cat's opposite (unfortunately for him) is a (male) dog, who unlike the Cat, is well meaning, slobbish, and has a very relaxed attitude towards life. The two crews decide to get to know each other at the disco while Holly and Hilly fix the Hop Drive. While the computers are at work, Dave and Arnold get to know their female selves. Ironically they are horrified by their female selves, showing identical traits to them but blind to their faults. Arnold is horrified and repulsed by Arlene's sexual advances towards him and finds her chat up lines pathetic. Dave thinks Debbie is a laugh but isn't impressed by her wanting to eat vindaloo and burping Yankee Doodle. The Cat is unsurprisingly unimpressed by the Dog, finding him lacking in small talk and is a terrible dancer. Holly and Hilly end up falling for each other, with Holly appearing on the monitor with Hilly's lipstick on his face.
The next morning, Deb and Dave wake up, and find out that they have slept with each other while drunk. Arlene, ironically sickened by the sight, hopes that Dave winds up pregnant. Arnold quickly figures out why Arlene directed that statement toward Dave; in this universe, the men give birth to the babies. Dave argues that it's impossible as he doesn't have the equipment, but Arlene and Holly point out that the physical laws of this universe apply to him while he's here... he could very well be in the club, much to the delight of Arnold. Dave is horrified at this fact, and is upset at Deb's defence (she argued that Dave should have used protection). However, Holly reveals that the Hop drive is fixed, and they need to get back to their universe immediately. After returning to their own universe, Lister uses a pregnancy test, and while waiting for the results, Holly realizes that if Lister is pregnant, he could give birth to the twins seen in the echoes from the future. The result of the test comes back and, to Lister's horror and Rimmer's delight, it's positive.
As available for viewing on the Series II DVD:
- Extended dialogue between the main characters and their parallel counterparts, additional gags.
- The events which occur immediately after this episode are detailed in the "lost episode" Dad, and explained in a brief opening scrawl in the first episode of the next series.
- This episode marks the final appearance of Norman Lovett, until Series VII's "Nanarchy"; and also the first appearance of Hattie Hayridge, who would replace Lovett as Holly in Series III-V.
- It is also the final appearance of the original Red Dwarf/JMC uniforms. For Series III, new costumes were designed for Rimmer and Lister. The Red Dwarf crew do wear similar (though not identical) uniforms in Series VIII.
- When the Cat says "Lister - Female opposite; Rimmer - Female opposite; where's mine?", it is one of only three times the Cat ever says the name 'Lister' on the show. The other times he says it are in Series V's The Inquisitor and Series X's The Beginning. Whenever he refers to Lister he calls him "buddy", "dormouse cheeks" or just "Hey, you".
- The "Tongue Tied" musical number evolved from a brief gag, to a full-blown song and dance sequence. Danny John-Jules (credited as "Cat") released his own version of the song in 1993. It reached #17 on the UK charts. It is also the first and only musical number by Howard Goodall to reach the Top 20 of the UK Top 40 Music Charts.
- The "Tongue Tied" routine was choreographed by Charles Augins, who played Queeg in the previous episode.
- This is the first episode that the Cat refers to Rimmer as "Goalpost Head".
- The title of this episode, "Parallel Universe", doesn't appear at the start as in others. Instead, we open with the Tongue Tied musical number. The Remastered version has the title appear after the song finishes. This is also the first episode to not include the standard opening sequence, and in fact the title Red Dwarf does not appear on screen until the very end of the closing credits.
- The concept of parallel universes will be revisited in Series VII when a parallel-universe version of Kristine Kochanski joins the crew.
- The Cat breaks the fourth wall when he first discovers the Dog, delivering several of his lines directly to the camera.
- This episode reveals that the skutters can 'breed', or at least self-replicate.
- In the first scene in Rimmer and Lister's quarters the Cat is wearing a different outfit, but immediately afterward wears the red outfit from the "Tongue Tied" number for the rest of the episode.
- There is in fact a musical group called The 5th Dimension, but they do not have a song called "Baby I Want Your Love Thing."
- Rimmer: You know -- cats have a very strange attitude toward women if you ask me.
Cat: Say what, Goalpost Head?
Rimmer: It's all sex, and no sense of settling down and having a long term relationship.
Cat: Hey, I want to settle down. And as soon as I find the right small group of girls, the seven or eight women who are right for me, my wandering days are over, buddy.
- Lister: What are you, a man or a munchkin?
Rimmer: I'm off to see the wizard...
- Holly: No, no, it has gone. The entire Solar System is missing!
Rimmer: Well, what is actually out there?
Holly: Nothing. Just space.
Rimmer: Holly, the thought occurs that we haven't actually reached Earth... The further thought occurs that we haven't actually budged a smegging inch!
- Angela Bruce as Deb Lister
- Suzanne Bertish as Arlene Rimmer
- Matthew Devitt as The Dog
- Hattie Hayridge as Hilly