The one with lots of greenscreening.
The end result of the former showrunner Philip Hinchcliffe getting even with the higher-ups in retaliation for being kicked out of the saddle by devouring the show's budget last season, Underworld is perhaps the most infamous case of No Budget on the classic series. Without the funds to create sets, most of the scenes portrayed in it are almost entirely reliant on Green Screen effects. The end result? What remains today one of the most hysterically shoestring episodes of the original run.
The TARDIS lands on a spaceship, the R1C, commanded by a man named Jackson. He and his Minyan crew are on a quest to recover their "race banks" from another ship, the P7E, which left a hundred thousand years ago to form a new colony. The Time Lords, who are seen as Gods by the Minyans, shared a form of regeneration with them but left when the Minyans turned on them. Jackson's quite surprised to see a God suddenly standing in the middle of his spaceship, but the team doesn't have time to be surprised, as the R1C is buried by a meteor storm. Rocks gather around the spaceship's gravitational field, instantly forming the beginnings of a planet. The Doctor helps them escape, and they crash into another small planet just as the serial's budget runs out.
Investigating the planet, the Doctor and Leela are awkwardly projected onto a photo background and find a system of caves that leads to the P7E, long ago buried by asteroids. The P7E's computer, Oracle, has gone insane and rules over the survivors of the Minyan crew with the aid of the robotic Seers. It allows Jackson to take the race banks, but the Doctor realises that they are just fakes, primed with fission grenades. The Doctor herds the P7E's descendants into the R1C and gives Jackson a rather grand What the Hell, Hero? speech for considering the quest more important than the actual people the quest was all about. After that, Four tricks Oracle into allowing him to take the real race banks, meanwhile returning the fakes via the Seers. The resulting explosion destroys the P7E and propels the R1C off on its voyage to Minyos II with the P7E's survivors.
- Agony Beam: Herrick is tortured for information using an Agony Beam. And a mind reader, apparently.
- A.I. Is a Crapshoot: Oracle is quite megalomaniacal and delusional, at one point claiming to have created itself from nothing.
- Artistic License Physics: Most physics in this episode depends on a rather substantially overestimated gravitational constant.
- Asteroid Thicket: Now with added gravity!
- Beneath the Earth: The reason for the episode's title, rather than, well, The Underworld.
- Buried Alive: Jackson fears this will happen when the spaceship first starts to attract rocks.
- Cargo Cult: Like in "The Face Of Evil", the descendants of a crashed spaceship ended up worshipping their own technology.
- Cold-Blooded Torture: Herrick is tortured to get the truth out of him.
- Cold Equation: The spaceship doesn't have enough fuel to carry all slaves, so Jackson decides to throw them all out.
- Continuity Nod: The Doctor claims not to have come up with the idea of the Trojan Horse.
- Deadly Gas: Used to "fumigate" an area of tunnel where a dissident is thought to be hiding.
- Death Is Cheap: Each of the Minyans has regenerated thousands of times.
- Department of Redundancy Department: The Minyan commander says "The quest is the quest" two or three times per episode.
- Earth-Shattering Kaboom: Two nuclear bombs are enough to blow the quite young and not really stable planet to bits.
- Energy Weapon: The weapons used are lasers combined with particle beams.
- Face Death with Dignity: When it turns out there's no escape, Oracle decides that its death is really only its own fault and calmly gives up.
- Faceless Goons: The guards. And even when they take off their helmets, their faces don't actually look like faces.
- Getting Smilies Painted on Your Soul: Leela and another character are about to fight, but a guard shoots them with a "pacifier" gun. Apparently the effects of the ray are to make people happy, so they stop fighting.
- A God Am I: Both the computer and the Time Lords.
- God Is Evil: This is how the Minyans view their Gods, at least. And the Time Lords are their Gods...
- Graceful Loser: After having spent the previous episode chewing on the scenery, the Oracle resigns itself to destruction with surprising dignity.
- Gravity Sucks: Played straight and then inverted when it is the R1C itself that is exerting too much gravitational force on its surroundings, sucking in smaller objects and becoming the core of a new planet.
- Heroic Sacrifice: Attempted by Herrick, but the Seers refuse to kill him.
- Human Sacrifice: Played with. The sacrifices aren't being made to appease some god, but to keep the slaves in check.
- Hoist by His Own Petard: The computer is blown up by its own bombs.
- Kick Them While They Are Down: The Seer does this to Herrick to verify he's alive for Cold-Blooded Torture.
- Luckily, My Shield Will Protect Me: The Minyans' guns are mounted on shields which also reflect beam attacks.
- Made a Slave: Most of the people on the planet are enslaved to labor. They think the "sky falls" (tunnel collapses) are done to keep their number low, just enough to labor.
- Negative Space Wedgie: The spiral nebula at the beginning of the episode.
- No One Gets Left Behind: The Doctor refuses to abandon the slaves to die.
- Oh, Crap!: "Two-thousand megatons?!"
- One-Word Title
- The Quest Is The Quest
- Really 700 Years Old: Each of the Minyans is about 100,000 years old.
- Reverse the Polarity: Justified in dealing with the Deadly Gas:The Doctor: What is blown can be sucked.
- Sarcastic Confession: The Doctor goes back to the planet to get rid of the fake race banks, which are actually bombs. He travels all the way back to where he can get captured again (rather than just leaving them on the surface) so it's obvious that he planned to have them taken from him, yet when forced to give them up, he explains that they are really bombs. "You can do better than that..." replies a villain and confiscates them. The bombs blow up the planet, of course.
- Shout-Out: Part one was broadcast only a few days after Blake's 7 debuted. Composer Dudley Simpson worked on both shows and, according to the DVD production notes, snuck a reference to the theme music into the score for the Underworld episode.
- Slow Light: The laser-guided particle beams go barely faster than walking speed. It's practically a wonder anyone gets hit with them.
- Sufficiently Advanced Aliens: The Time Lords are this to the Minyans.
- Technology Uplift: The Time Lords to the Minyans in the backstory.
- Trojan Horse: The Doctor and Leela hide in a minecart, referencing the myth of Troy. Then the Oracle uses the same trick, disguising bombs as the data cylinders.
- We Want Our Jerk Back: The Doctor quickly gets irritated by calm peaceful Leela, and hypnotizes back her familiar savage self.
- Whole Plot Reference: To the quest for the Golden Fleece. The Doctor explains the whole thing to Leela after he accidentally called Jackson "Jason".
- You Shall Not Pass!: When the crew are being chased by the guards, Herrick stays behind to let the others escape.