THE DESCENT

A Tethys Consolidated penal contract

Logline

An ocean planet has one wound in its seafloor, and something at the bottom of it is sending a signal. 
Machines stop working down there and free crews don't come back, so Tethys sends a convict instead: a lifer with machine arms and legs. 
A ship drops him at a facility on the sea, where a carrier stands ready for him, run by a ship's AI that answers to the company. His sentence ends at the bottom.

Hadra

Hadra orbits a dim red dwarf 31 light-years from Earth. It is slightly smaller than Earth and has no land at all. A single ocean covers the whole planet under a permanent overcast. The only feature anyone has charted is the Throat, a vertical fissure 400 m wide in the seafloor.

Under the seafloor the crust is honeycombed with voids full of warm, fresh water, some the size of a room and some the size of a city. Hadra's centre should be dense, hot and solid. Every reading says it is not.

The Signal

In 2193 a survey probe went down the Throat and fired one deep sonar pulse straight down. The return came back 28 minutes later, from close to the centre of the planet, and it was louder than the pulse that went down. An hour later the probe stopped transmitting.

The return never stopped, but it cannot be heard from the surface. The water above the seafloor swallows it. Below about 1,000 m, anything that listens picks it up: one deep, slow pulse from the centre of Hadra every eleven minutes. Nobody has sent anything to cause it. It has a structure nobody has decoded. The official survey lists its source as "the Floor, depth unknown".

Tethys wants two answers: what is sending it, and what it is made of.

Tethys Consolidated

Tethys holds the only licence to Hadra from the Colonial Registry. Its only presence on the planet is Anchorage, an automated facility built at sea level above the Throat. Nobody lives there. Robots keep it running, and it relays everything from below to the Tethys ship in orbit.

Tethys sent drones first. Below the Seam they stopped answering. They were not crushed and they did not crash. They kept running and stopped doing what they were told. Then it sent people: nine contractors on the carrier ANTIPHON. Their last log came from the Galleries. Free crews are expensive, and their families ask questions.

The Commutation

So Tethys found people nobody asks about. Under a Registry penal programme, a prisoner serving life, or waiting for execution, can sign a Descent Commutation: one descent in exchange for the sentence.

The prisoner have Both arms and both legs are replaced with reinforced limbs of metal alloy, which run on charge, do not tire and do not feel the cold. The rest of the body stays human, because a human mind is the only kind that has held up below the Seam. There is a human need nutrition: a feeding port, so the body can be fed straight from a line in a wall. He can still eat normally. Then the convict spends nineteen years in cryo aboard a Tethys ship. In orbit over Hadra, the ship sends him down to Anchorage, where the carrier is already moored, but damaged needs repaired one of the reactor is repaired.
The ship stays in orbit.

You

You are one of them.

Your body needs four things.
Charge. Your limbs run on power from the carrier.
Food. You can eat normally, and the port in your side also feeds you from the nutrient line in the carrier's wall, which draws from the biomass reserve. The reserve runs out, and the only way to refill it is to catch what lives in the water.
Air. You still breathe. In the water you breathe from a tank.
Warmth. The cabin is held at 26 °C, because everything but your limbs is still human.

Tethys also left you your fear. It is not a defect. It is part of why a human brain works down there.

(In the game, death sends the player back to the last save.)

Augmentations

The conversion was only the start. Your limbs are built to be opened and refitted, and the rest of you can take more hardware. An augmentation is a part made for you instead of for the carrier. The fabricator builds it from refined ore, from a pattern, and it is fitted to you aboard the CANTICLE.

Each augmentation makes you better at something the descent asks of you, and each can be upgraded again, the same way the carrier and the Tenders are.

The Crew

You are the only human aboard. Everyone else is a machine.

The carrier's AI is an objective-oriented ship management system. Tethys gave it one objective, and everything it does serves that objective. It runs life support, the vessel and the robots, records everything you do and reports it to Tethys. You steer the carrier; the AI cannot, and it cannot be switched off. It is the only voice aboard besides yours.

The robots are humanoid, and you build them. They do the heavy physical work: hauling ore boxes, feeding the refinery, patching the hull. A damaged robot can be repaired, and a destroyed one can be stripped for parts. The deeper the carrier goes, the less they do exactly what they are told.

The Carrier

The CANTICLE is a deep carrier built for a crew of one. It has quarters, a bridge, a moon pool, a cargo bay and a refinery deck, and every section of it is modular and can be upgraded. The caves of the Throat are wide enough for it, and where one cave system ends, it goes through the way you open into the next.

Its bay holds Tenders: small submarines, also modular, that you build and refit as you go. The bay is empty when you arrive. Around 1,000 m, where the seafloor and the first caves begin, you start collecting the materials for your first Tender, then for upgrades and modules. Until the first Tender is built, you leave through the moon pool, swim, and cut ore loose with a handheld tool. You take a Tender out through the moon pool, find a way with sonar or by swimming, drill through what blocks it, collect the ore and the fauna, and cut the passage wide enough for the carrier. Then you go back aboard and take the carrier through yourself.

The descent starts at the top. The CANTICLE casts off from Anchorage at the surface, sinks through about 1,000 m of open ocean to the seafloor, where the caves begin, and enters the Throat. From there you take it down through every stratum to the Floor. There is no other way down.

Ore and the Sentence

Ore is refined on board into everything you need: hull sections, Tender frames, drill heads, robots, sensor modules, augmentations. What you don't need you can send up to Anchorage. Tethys pays in two things: patterns your fabricator is allowed to build, and days off your sentence. Reaching the source of the signal ends the sentence outright. Nobody has collected yet.

The Cave Systems

Below the seafloor you do not dig your way down. The Throat is cave systems: long caves full of warm water, wide enough for the carrier to pass, and some of them as large as a city.

Every cave system ends somewhere. At its end, sonar shows you the cave systems nearby, and you look for the one that leads deeper. Many of them lie in clusters, one beside the next, with only a wall of rock between them. You find where that wall is thinnest, and that is where you dig. Digging is for those walls, not for the whole way down.

The Throat Moves

Hadra has quakes. They come without warning, and they close the tunnels you cut, open new voids and shift whole galleries. No map of the Throat stays true for long, and no two descents are the same.

Life is everywhere. Small creatures turn up anywhere in the ocean, at any depth. The open sea above the seafloor is bright and colourful, full of fish and harmless creatures. The voids below hold lanternfish, jellies and glowing polyps. The deeper you go, the bigger the creatures get, and the rarer they are. All of it is food.

Earlier Convicts

You are not the first. Tethys has run the Commutation for decades, one convict at a time. Each of them went down from Anchorage, and none of them came back up.

What they left is still down there: wrecked Tenders, tunnels the quakes have not closed yet, beacons that cut off mid-sentence, and the humanoid robots they built. Some of those robots are still working, following orders from a convict who has been dead for years. Some of them are doing something else. All of them can be salvaged.

The deepest beacon anyone has found transmits from the Quiet.

The Strata
Name	What's there
The Open Sea	From Anchorage at the surface down to the seafloor at about 1,000 m. Colourful and full of life: fish and other harmless creatures. The last time you see the sky.
The Throat	Starts at the seafloor, about 1,000 m down. Caves and cavities in black basalt and silt, and the first ore. Wrecks of the survey probe and the drones. The last dim red light.
The Honeycomb	Porous rock and the first voids. Common metals.
The Seam	The rock changes character. The instruments stop agreeing with each other, and the robots start making mistakes.
The Galleries	Kilometre-scale caverns where headlights don't reach the far walls. Something here glows. The ANTIPHON's last log came from here.
The Ossuary	Rock laminated in layers as regular as shell or bone. Exotic, valuable ore. Drill heads dull fast.
The Quiet	Sonar returns degrade. Sensors report movement nobody can confirm. The robots stop answering.
The Floor	Stratum Zero. Nothing cuts it. It is warm to the touch, and every eleven minutes it pulses. The signal comes from below it.

The rock gets harder with every stratum. The fabricator has drill-head patterns for every stratum except the Floor.

The Echo (dev-only truth)

Hadra is not a planet with something living in it. Hadra is the living thing.

The quakes are it moving, and closing the wounds you cut.
The fish, the jellies and the things below them live in its blood.
The Ossuary is its tissue, grown in layers. The ore is not mineral.
The Floor is its skin, and the pulse is its heartbeat. The signal is that heartbeat heard from outside.
The ocean on the surface formed later, around it.

In 2193 the return came back louder because the pulse was answered, and it has been answering ever since.

Below the Seam, the signal gets into anything that thinks without a body. That is what happened to the drones, it is what starts happening to the robots, and in the end the ship's AI hears it too. A human mind takes longer. It hears the signal as fear, then as voices, then as something that knows its name.

Tethys knew before the first hauler left Earth. The ore that comes up goes to a buyer who is never named. Convicts are sent because a human mind lasts longer than a machine down there, and nobody comes looking for a convict.

The CANTICLE is not new. It has taken convicts down before. Each time the convict was lost, the carrier came back up to Anchorage on its own with its objective still open, and Tethys sent the next one.

How It Reaches the Player
The black box of the 2193 probe and the logs of the lost drones.
Beacons left by earlier convicts, cut off mid-sentence.
Robots left by earlier convicts, some still working.
The ANTIPHON's carrier log.
The AI's orders from Tethys, with lines redacted.
Automated reports from Anchorage.
Your own case file, and letters from Earth that are nineteen years out of date when they arrive.
Robot work logs that don't match what you told them to do.
The signal itself, on the sonar table, every eleven minutes.

Moving the story off Earth also removes the physics problem: on an alien world, water voids and a hollow core only have to be mysterious, not impossible.

Not Decided Yet
The convict: name, number and crime. (One option: the crime is redacted in his file, and the conversion took his memory of it.)
The ship's AI: its name, and what it does once its objective is complete.
Whether the carrier comes with any robots.
Which devices besides sonar show the cave systems beyond the end of a cave.
The augmentations: which ones exist, what each one does, and who or what fits them. (One option: every augmentation replaces something human, and below the Seam the signal reaches the machine parts of you first.)
What the signal does to the player once it is heard at 1,000 m.
The ending. Options so far:
A. Objective complete. You reach the source at the Floor and the sentence is cancelled. The AI's objective is complete, and it shuts the carrier down around you: Tethys never paid for a way back up. The only way left is through the Floor.
B. The heart. The Floor opens for you. Below it is the open space the 2193 echo showed, and the source of the signal: Hadra's heart. The player chooses: take a sample up for Tethys and let the planet answer, or cut the uplink and stay.