The Underbelly

“The Hidden Empire”

“You’ve heard of the Black Sky Cartel. You’ve traded with them, feared them, maybe even worked for them. But you’ve never seen their heart. No one has. Except The Captain.”
—Whispered rumor

Quick Reference

The Underbelly - The Hidden Empire

Overview

The Underbelly is the worst-kept secret in the Aetherium: everyone knows the Black Sky Cartel has a headquarters somewhere in the deep Murk, but no one knows exactly where. Not the Sky-Guild. Not Ironhold’s military. Not even most Cartel members—they’re brought blindfolded, navigate by memorized routes, or simply never go there at all.

The Captain runs the entire Cartel from this hidden fortress, coordinating smuggling operations, black market trade, and criminal enterprises across the Aetherium. Orders flow out through trusted lieutenants. Profits flow in through complex laundering networks. And The Captain remains invisible, a ghost directing an empire of shadows.

The Underbelly itself is built for concealment: structures hang from the island’s underside (inverted architecture), chambers are carved into the interior, and docks hide in natural caves. The island is surrounded by dense Rot-clouds that obscure vision and deter casual exploration. Corrupted Rot-Beasts patrol the perimeter—some say they’re controlled, others say they’re just tolerated, but either way they serve as effective guards.

Only Cartel core members live here permanently—lieutenants, elite smugglers, guards, and essential support staff. It’s not a city; it’s a headquarters. A command center. A throne room for the criminal underworld’s invisible monarch.

The Underbelly’s location is protected by layers of misdirection, false rumors, and lethal consequences for anyone who gets too close. Cartel members who betray its location don’t just die—they disappear so completely that even their names are forgotten.

Geography and Structure

The Island

Size: Estimated 1.5-2km diameter (medium-large)

Shape: Irregular, with deep natural caves and overhangs

Terrain: - Rocky, unstable surface (deliberately unmaintained) - Dense corrupted vegetation (camouflage) - Natural cave systems (extensive) - Underside structures (inverted architecture)

Rot Status: - Stage 2-3 corruption (moderate to heavy) - Residents adapted or corrupted - Rot-clouds provide concealment

Location: - Deep Murk (exact coordinates secret) - Estimated 300-400km from Skyport Eos - Surrounded by corrupted islands (natural barrier) - Drifts slowly (position changes)

Concealment Methods

Natural: - Dense Rot-clouds (visibility <50m) - Corrupted islands nearby (deterrent) - Rot-Beast activity (danger zone) - Deep Murk location (rarely traveled)

Artificial: - Minimal surface structures (appears abandoned) - Inverted architecture (hidden from above) - Interior chambers (invisible from outside) - Hidden docks (cave entrances) - False landmarks (misdirection)

Operational: - Blindfold protocols (visitors) - Changing routes (confusion) - False rumors (misdirection) - Lethal security (consequences)

Architecture

Surface Level (deliberately deceptive): - Appears abandoned or corrupted - Ruined pre-Shattering structures (fake) - Corrupted vegetation overgrowth - No obvious habitation

Underside (inverted structures): - Buildings hang from island bottom - Chains and anchors secure structures - Platforms suspended in void - Living quarters, warehouses, workshops - Accessible by interior passages

Interior (carved chambers): - Extensive cave network (natural + excavated) - The Captain’s quarters (location unknown even here) - Command center - Secure storage (high-value goods) - Prison (for special prisoners) - Meeting halls

Key Locations

The Captain’s Sanctum

Location: Unknown (even to most residents)

Description: The Captain’s personal quarters and command center

Access: By invitation only (extremely rare)

Security: Absolute (multiple layers)

Function: - Strategic planning - High-level meetings - The Captain’s private space

Mystery: No one describes it the same way (deliberate misdirection? Multiple locations?)

The Counting House

Location: Interior chamber, central

Function: - Financial operations - Profit distribution - Laundering coordination - Records (encrypted)

Staff: - Accountants (trusted, well-paid) - Couriers (discrete) - Guards (lethal)

Security: Second only to Captain’s Sanctum

The Shadow Docks

Location: Natural cave system, multiple entrances

Function: - Ship arrivals/departures - Cargo handling - Maintenance - Emergency escape routes

Features: - Hidden from external observation - Multiple entrances (redundancy) - Underwater passages (some) - Defensive positions

Capacity: 30+ ships (various sizes)

The Vault

Location: Deep interior, heavily guarded

Contents: - High-value stolen goods - Contraband (Rot-Shards, forbidden items) - Emergency funds - Blackmail material - Weapons cache

Security: - Elite guards (24/7) - Complex locks - Trapped approaches - The Captain’s personal oversight

The Barracks

Location: Underside structures

Population: ~400 guards and soldiers

Function: - Security force housing - Training facilities - Armory - Ready response

Discipline: Military-grade (Cartel elite)

Population and Society

Demographics

Core Members (~500): - Lieutenants (The Captain’s inner circle) - Elite smugglers - Accountants and administrators - Master criminals

Security (~400): - Guards (trained, loyal) - Soldiers (military-grade) - Enforcers (special operations)

Support (~600): - Craftspeople (ship repair, weapons) - Servants (cooking, cleaning) - Families (some) - Specialists (various)

Total: ~1,500 (estimated)

Hierarchy

The Captain: Absolute authority, invisible ruler

Lieutenants (5-7): - Vex Shadowhand (operations, Murky Chasm) - Others (names unknown to outsiders)

Captains (20-30): Ship captains, operation leaders

Crew: Smugglers, thieves, muscle

Support: Everyone else

Culture

Secrecy: Paramount value (betrayal = death)

Loyalty: To The Captain, enforced absolutely

Competence: Valued (incompetence is liability)

Pragmatism: Morality irrelevant, results matter

Discipline: Surprisingly high (chaos is bad for business)

Rules

The Captain’s Law: 1. Secrecy absolute (location, operations, The Captain’s identity) 2. Loyalty enforced (betrayal = disappearance) 3. Competence required (failure has consequences) 4. Profit shared (fair distribution maintains loyalty) 5. No internal conflict (settle disputes through channels)

Enforcement: Swift, lethal, thorough

Economy

Criminal Operations

Smuggling: - Forbidden goods (Rot-Shards, weapons, contraband) - Tax evasion (bypass Guild tariffs) - Illegal passengers (fugitives, exiles)

Black Market: - Coordination of illegal trade - Price setting - Territory management

Theft: - High-value targets - Commissioned jobs - Fencing operations

Extortion: - “Protection” services - Information brokering - Blackmail

Other: - Assassination (rare, high-value) - Sabotage (commissioned) - Espionage

Financial Network

Income: Millions in trade value annually (estimated)

Laundering: Complex networks through legitimate businesses

Distribution: - The Captain (40%) - Lieutenants (30%) - Operations (20%) - Crew (10%)

Reserves: Substantial (exact amount unknown)

Defenses

Location Security

Primary Defense: Secrecy (location unknown)

Secondary: - Rot-clouds (concealment) - Rot-Beasts (deterrent/guards) - Corrupted islands (barrier) - False trails (misdirection)

Military

Guards: 400+ trained fighters

Equipment: - High-quality weapons (stolen or purchased) - Armor - Airship weapons

Training: Military-grade (many ex-soldiers)

Discipline: High (professional criminals)

Response Protocols

Intrusion: - Immediate response (guards) - Capture if possible (interrogation) - Kill if necessary (no witnesses) - Disposal (bodies disappear)

Discovery: - Evacuation plans (multiple routes) - Destroy evidence - Relocate if necessary (prepared)

Betrayal: - Hunt traitor (relentless) - Eliminate (thoroughly) - Erase (name, history, everything)

Notable Residents

The Captain

Role: Absolute ruler of Black Sky Cartel

Identity: Unknown (completely)

Presence: Invisible but felt everywhere

Authority: Unquestioned

Vex Shadowhand

Role: Lieutenant, operations in Murky Chasm

Relationship: Trusted (one of few who meet The Captain)

Function: Public face of Cartel operations

The Accountant

Name: Unknown (called “The Accountant”)

Role: Financial operations

Reputation: Brilliant, ruthless with numbers

Loyalty: Absolute (well-compensated)

Master-at-Arms Krell

Role: Security chief

Background: Ex-Ironhold military (disgraced)

Personality: Professional, brutal when necessary

Loyalty: To The Captain (personal)

Current Situation

Operations

Status: Thriving (Cartel at peak power)

Expansion: Growing influence across Aetherium

Competition: Minimal (Cartel dominates criminal underworld)

Threats: - Sky-Guild enforcement (increasing) - Ironhold military (occasional raids) - Internal betrayal (constant vigilance)

The Captain’s Plans

Unknown: The Captain’s long-term goals unclear

Speculation: - Pure profit? - Political power? - Survival strategy? - Something else?

Observation: Operations becoming more sophisticated, organized

Secrets and Mysteries

The Captain’s Identity

Mystery: Who is The Captain?

Theories: - Former Guild-Master - Exiled noble - Rot-Touched prophet - Multiple people - Something inhuman

Evidence: None conclusive

The Rot Connection

Observation: Rot-Beasts don’t attack Underbelly

Theories: - The Captain controls them - Mutual understanding - Coincidence - The Captain is Rot-Touched

Reality: Unknown

The True Location

Knowledge: Exact coordinates unknown

Estimates: Deep Murk, 300-400km from Eos

Misdirection: Dozens of false locations circulated

Reality: Changes (island drifts, or multiple locations?)

Quest Hooks

1. The Search: Hired to find Underbelly (impossible task?)
2. The Invitation: Summoned to meet The Captain (why you?)
3. The Escape: Prisoner in Underbelly (escape how?)
4. The Betrayal: Cartel member wants out (help them?)
5. The Raid: Military planning attack (guide? Sabotage?)
6. The Deal: Need something only Cartel can provide
7. The Identity: Discover who The Captain really is
8. The Infiltration: Go undercover in Cartel (dangerous)

GM Notes

Using The Underbelly

Purpose: Criminal headquarters, mystery location

Tone: Dark, secretive, dangerous, organized

Function: Cartel operations center, plot device

Mystery: Keep location and Captain’s identity ambiguous

Potential Arcs

The Discovery: Players find Underbelly (consequences?)

The Revelation: The Captain’s identity revealed (shocking?)

The Fall: Underbelly destroyed/discovered (Cartel collapses?)

The Alliance: Temporary cooperation with Cartel (moral complexity)

Related Topics

• The Captain
• Vex Shadowhand
• Black Sky Cartel
• Murky Chasm
• The Murk

“The Underbelly exists. Everyone knows it. But knowing it exists and finding it are very different things. And finding it and surviving are even more different.”
—Sky-Guild investigator

“I’ve been to the Underbelly three times. Each time, different route, different appearance, different location. Either it moves, or there are multiple sites, or I’m being deliberately confused. Probably all three.”
—Vex Shadowhand

“The Captain sees everything. Knows everything. Controls everything. From a place no one can find. That’s not just power. That’s something else entirely.”
—Cartel member (anonymous)