While cruising through space in Starbug, the Dwarfers find that they gone off course from their path back to Red Dwarf (thanks to Lister falling asleep at the wheel), and find themselves in "Vampire GELF" territory. The Cat becomes terrified when he hears that Vampire GELFs feed on the blood of virgins, though hastily tries to deny this, claiming he has "two lady cats" on Z Deck.
While correcting their course, they spot a ship about to fall into a black hole. Learning that the ship is populated by a "Mercenoid" and an organic prisoner, the crew mounts a rescue. After a brief confrontation, the Mercenoid is killed, and the prisoner is located. The prisoner is revealed to be a female Felis Sapien, to the Cat's delight, and is brought back to Red Dwarf, where the cat plans a date with her, culminating in him finally having sex.
Soon after, Kryten discovers that the "lady cat" is actually a Polymorph, disguised as a Felis Sapien. By the time the rest of the crew alert the Cat of this, he has already been impregnated with the Polymorph's offspring. All attempts to remove the Morphling eggs before they hatch prove futile, leaving the crew no choice but to allow them be born. Afterward, they try to dispose of them, but the Cat, having been affected by a pheromone the Morphlings produce, runs off with them instead.
In an attempt to take out the Morphlings before they are fully grown, Kryten uses a "personality tuck" machine they had salvaged from a medical frigate earlier to remove Lister's emotions, making him practically invisible to the Morphlings. Lister succeeds in killing two of them, but the others pose as the rest of the crew members, sowing confusion and paranoia until the Cat shows up and kills all the remaining Morphlings.
That night, Lister comes to talk to the Cat, telling him that being a virgin isn't such a bad thing (hastily adding that he doesn't think he is). After Lister leaves, two lady cats pop up in bed with the Cat. One of them points out that the Cat is just dreaming this, but the Cat doesn't care.
"Can of Worms" contains examples of:
- Ambiguously Evil: The mercenoid which appears during the episode. It attacks the Dwarfers, appears to be keeping a Felis Sapien as a prisoner, and, judging by Lister's comment about it's race, appears to be a member of yet another race of robots that are nuts. However, its actions take on a different light once it's revealed that it's actually keeping prisoner and trying to kill a Polymorph instead.
- Bounty Hunter: The "Mercenoids" fill this quota.
- Continuity Nod:
- The Cat's old "That's mine, this is mine" routine from season 1 makes a return.
- The crew once again encounter a Polymorph.
- Cuteness Proximity: The baby polymorphs use this as a defence mechanism by turning themselves into incredibly cute animals to convince people not to kill them. Well, a person. Lister is taken in by them, despite Kryten trying to warn him of what the polymorphs will do if they are not killed immediately.
- Death Seeker: Mercenoids are droids who voluntarily agree to give their lives in exchange for a place in Silicon Heaven.
- Deceptively Cute Critter: Baby Polymorphs are capable of turning into adorable animals as a defense mechanism, preventing people who would normally throw them out into Deep Space due to their nature of being an Emotion Eater to take pause.
- Emotion Eater: The Polymorphs, as usual.
- Emotion Suppression: Kryten uses the "personality tuck" machine to remove Lister's emotions, making him practically invisible to the Morphlings.
- Fooled by the Sound: The crew is threatened by a Mercenoid (which is a member of a race of robotic bounty hunters). To divert it, Lister throws Rimmer's dictaphone, which is playing recordings of Lister's voice, away from them in a bid to distract the Mercenoid. The ruse is seemingly revealed when the recordings of Lister's voice end and those of Rimmer's start up. However, it is then revealed to be a ploy to get the Mercenoid to pick up the device and get electrocuted.
- The Ghost: Although they're discussed by the Dwarfers at the start of the episode, the Neki-Nenkas (basically Vampire GELFs), make no appearance at all during the episode.
- Girlfriend in Canada: The Cat insists that he has two felis sapiens girlfriends on Z Deck, who prefer to avoid the other Dwarfers. Nobody believes him.
- Gone Horribly Wrong: Removing Lister's emotions turns him into an unempathetic killer who doesn't bat an eye at the thought of accidentally killing the Cat.
- How Did You Know? I Didn't: When the emotionless Lister kills a Polymorph posing as the Cat, he provides this rationale.
- Inverted Trope when Cat ends the episode gunning down all the Dwarfers' doubles in the end. "A momma always knows."
- Mexican Standoff: A trio of them occurs at the climax of the episode with Rimmer, Lister, Kryten, and the morphlings who are disguised as the trio all holding each other up with Guns Akimbo. The Cat ends up resolving it by shooting all the morphlings.
- Mister Seahorse: The Cat is impregnated with Morphling eggs.
- Never Trust a Trailer: The publicity for this episode avoided mentioning the return of the Polymorph, and suggested it was going to be a story about the Cat falling in love with another of his own kind.
- Nice Job Breaking It, Hero: The Mercenoid was trying to dispose of the Polymorph by flying his ship into the black hole, but the Dwarfers inadvertently ruined his plan.Lister: Our nomination for "JMC Crew of the Year" is looking rather poor right now.
Rimmer: Those damn monkeys on the Omega 3 will likely get it again. - Of Course I'm Not a Virgin: The Cat tries to invoke this. The others don't believe him, but humor him anyway.
- Oh, Crap!: The Cat's reaction when Rimmer says the vampire GELFs feed on virgins.
- Read the Freaking Manual: For a quick gag before the plot takes off, Rimmer is on radar duty while the others board the Mercenoid's ship. He spots movement aboard the ship, organic and part organic moving in "Corridor Beta 12, South Entrance". Only, that's where the others are. He tells them to run, but the movements are erratic, they are reacting to the Dwarfers' movements until Lister stops and asks... if the life signs Rimmer see are actually them.Rimmer: Ah, yes. "Organic and part organic", yes it's you. They really should mention that in the instruction manual, someone could look like a real idiot not knowing it. (Actually reads the instructions) Ah. It does mention it. Right here, in big red capitals. So easy to miss.
- Stylistic Suck: Despite the series previously having used much more convincing (well, for the time) morphing effects for the Polymorph's cousin, the Emohawk back in Series VI, the Morphlings' changing forms is depicted using the same jump-cut technique used back in the first appearance of the species all the way back in Series III.
- Teeny Weenie: Heavily implied in Rimmer's dictaphone with the line "Size does not matter." Rimmer goes pale when it plays out loud in front of the others.
- There Is Another: Subverted. The crew initially appear to have come across another specimen of the Cat's species, being held prisoner by a mercenoid. It turns out to actually be a female polymorph.
