The Gate
The Gate
Read aloud
For three weeks, Kelpstrand's warm channels have run colder, and each evening the stone beneath the settlement gives a slow, heavy knock. The current-keeper offers you access to the old gate works, along with a surveyor's ledger and a bundle of maintenance tools. Before another pulse shakes the channels apart, someone must find what is choking the flow.
Run the session
Cheat sheet
Objectives
- 1Prepare for the descent by securing the old records and repair tools.
- 2Find the obstruction and understand what is straining the gate.
- 3Stabilize the gate before accumulated pressure breaks it.
- 4Leave the cavern's ancient resident alive and at ease.Optional
The clock
The Gate Chamber Pressure track begins at 2 and rises on initiative count 20 while the fitting remains attached. Each surge drops Pressure to 2 but adds one Crack; at three Cracks, the gate fails. Once the fitting is removed, Pressure rises every other round. Each successful easing action reduces Pressure by 1, subject to the listed limits.
Scenes
- 0:00A Current Gone Thin
- 0:45Station 4
- 2:00The Pulse Below
- 2:45The Gate Chamber
- 4:15Warm Water, Open Questions
Cast
- Mara VennQuestgiver
- Halden RuskAlly
- Ilyra SennWitness
- Old KettleWildcard
The hook
Set the scene
Read aloud: The ladder ends in a cavern broad as a harbor hall. Warm water rushes through the lower half, carrying the smell of minerals and wet stone beneath a low ceiling of black rock. Across the north walkway, a house-high slab stands in its frame, held by wrist-thick chains; beyond it, water boils white. Each slow pulse shudders through the cavern, and a rime-grey fitting hums against the gate.
How Mara Venn asks
Mara Venn approaches the party at Kelpstrand's current-house, where a basin of channel water sits cold against the palm.
She offers the old surveyor's ledger, Station 4 tools, and whatever local assistance the party needs, asking them to inspect the gate before the next pulse damages the channels.
Rumours
Scenes
about 5 hours0:00
45 min
socialThe table is here
1. A Current Gone Thin
Kelpstrand's current-house, beside a stone basin of water that feels noticeably cool.
Mara Venn explains the cooling current, the old gate, and the risk of waiting. Halden can lend the ledger, while Ilyra describes the last failed attempt to reach the lower works. Let the party ask questions, gather food, and choose who carries the tools.
NextWhen the party accepts the work, Halden opens the ledger to a marked route and leads them toward the service stair, where the sound of rushing water grows louder below.
0:45
75 min
exploration
2. Station 4
A submerged service passage with mineral shelves, a narrow dry ledge, and a tool cache behind a jammed grate.
The party follows the ledger through a flooded maintenance run, crossing silted passages and locating Station 4's tools. They can bypass, evade, or fight the pressure-warped cave lurkers. Searching the station reveals that the gate's flow marks are still legible, but the oldest maintenance notes end abruptly.
The Silted Service RunNextWith the tools secured and the ledger's route confirmed, the passage slopes down toward a ladder. Warm spray beads on the rungs, though the stone around the waterline is growing cold.
2:00
45 min
exploration
3. The Pulse Below
The ladder landing at the edge of the gate chamber, dry and safe from surges.
Ilyra's account is confirmed by fresh marks on the stone: something has been drawing heat in irregular pulses. Characters can inspect the gate from the landing, identify the three clogged weep-holes, see the chain winch, and spot the fitting high on the housing. A successful Intelligence (Arcana) check after removal reveals that it has been drawing heat; a check notices the hidden struck-through spiral.
NextAs the party leaves the landing, the next heavy pulse rolls through the cavern. Water slaps the walls, and a huge basalt-plated shape raises its head from the warm shelf.
2:45
90 min
skill
4. The Gate Chamber
The 80-foot gate cavern, with warm water 4 feet deep, a north-wall walkway, the dry landing, the gate housing, the weep-holes, the fitting, and Old Kettle's shelf.
Run the gate chamber as a race against pressure, not a battle the party must win. Pressure begins at 2. On initiative count 20, it rises by 1 each round while the fitting is attached, and by 1 every other round after removal. At 6, resolve a surge: creatures not on the ladder landing make a Dexterity saving throw, taking 7 () Fire damage on a failure or half as much on a success; Pressure drops to 2 and the gate gains one Crack. Three Cracks mean the gate fails. Successful easing actions each lower Pressure by 1: free the chains with Strength (Athletics), or Dexterity (Sleight of Hand) using the Station 4 tools; clear each of three weep-holes once with Strength (Athletics); read the safe-flow marks with Intelligence (Investigation), or with Halden's ledger, granting advantage on the next two easing checks; or calm the water with Wisdom (Survival), lowering Pressure by 1 for one round only, without stacking. Removing the fitting takes an action and a successful Intelligence (Arcana) or Dexterity (Thieves' Tools) check. At Pressure 4 or higher, removing it triggers a surge immediately. At 3 or lower, it comes off cleanly. A failed removal check does not trigger a surge, but the character takes 3 () Cold damage. On the second round of the pulse, Old Kettle wakes and rolls initiative. It attacks the closest creature only if it has been threatened or its home has been damaged. A Wisdom (Animal Handling) check calms it for 1 minute; a second check can extend that calm. Food or a warmth effect on the water grants advantage. Two rounds after the fitting is removed, Kettle calms without a check as the water warms. The chamber encounter ends when the fitting is removed, all three weep-holes are clear, the chains are free, and Pressure is 2 or lower.
The Gate ChamberNextAs the last chain comes slack and the pressure eases, the gate's knocking falls out of rhythm, then stops. The water begins to run evenly past the stone, and the party climbs toward the waiting settlement.
4:15
30 min
social
5. Warm Water, Open Questions
The current-house and adjoining channels, where steam begins to rise again from the stone gutters.
Mara and the workers of Kelpstrand meet the party at the upper works. If the gate is stable, they feel the returning warmth in the channel and make plans to restore the routine inspections. If the gate failed, they begin evacuation and rationing while asking the party to help decide what can still be saved.
NextAs Kelpstrand's people move to reopen the channels, the party carries the strange cold fitting into the daylight and decides what to do with it.
Behind it
What people believe
Kelpstrand's current has grown colder and more erratic, and the old gate beneath the settlement has begun to shudder.
The current-keeper is sending a small crew to inspect the lower works, recover the survey records, and restore the gate's flow before the channels fail. The route is hazardous, and the gate chamber may hold dangers that have not been seen for generations.
Background
Kelpstrand's warm current is controlled by a centuries-old stone gate beneath the settlement.
The gate has begun to pulse out of rhythm, and its channels are losing heat. The trouble is concentrated at the gate chamber, but the tools, route marks, and records needed to work safely are scattered along the approach. This adventure is designed for three or more sessions, with the final session centered on the pressure-driven gate chamber.
The stakes
If the gate is stabilized, Kelpstrand's warm current returns to a steady flow.
If pressure breaks the gate, the settlement loses its reliable channel system, forcing urgent rationing, evacuation, and a dangerous future repair. Old Kettle's survival and trust depend on whether the party recognizes that the beast is reacting to a hostile change in its home.
Encounters
2The Silted Service Run
Combat, avoidable
A maintenance passage below Kelpstrand, with waist-deep warm water, a narrow ledge, and pockets of soft silt. A creature moving through the silt must succeed on a DC 12 Strength (Athletics) check or have its speed reduced to 0 until the end of its turn.
Foes
Two pressure-warped cave lurkers, use suitable low-CR beasts or custom creatures appropriate for four 3rd-level characters
ComplicationFlooded approach passages, confusing maintenance marks, and unstable footing make haste costly. Use the d6 complications table when the party stalls, makes noise, or pushes through a hazardous stretch.
ScalingFor a smaller or less experienced party, use one lurker and make it flee after taking damage. For a stronger party, add one lurker or place the encounter in deeper water. These are hazards of the damaged works, not agents responsible for the gate trouble.
The Gate Chamber
Combat and skill challenge, with a pressure hazard
An approximately 80-foot-wide cavern with warm water 4 feet deep, a north-wall stone walkway, and five working areas: the safe ladder landing; the gate housing 30 feet across the walkway; three clogged weep-holes on the south wall; the fitting 15 feet above the water; and Old Kettle's warm shelf at the east end.
Foes
Old Kettle, use its established Chapter 4 stat block
ComplicationThe party must divide attention between repair tasks and the rising Pressure track. Old Kettle's attacks should focus on nearby creatures that threaten it or its nest. It does not pursue characters on the ladder landing and can be calmed or pacified by fixing the cause of its distress.
ScalingFor four 3rd-level characters, the supplied Old Kettle encounter is a moderate-to-high challenge when the surge hazard is included. For a smaller party, allow it to be calmed with one successful DC 14 Wisdom (Animal Handling) check, or have it spend its first turn withdrawing to the shelf. Do not make Kettle's defeat necessary. A party that calms it earns the full 1,100 XP.
Cast
4Mara Venn
QuestgiverQuestgiver, Kelpstrand current-keeper
WantsKeep Kelpstrand's channels warm while ensuring the repair does not endanger the people who depend on them.
“The current has carried Kelpstrand through worse winters, but I will not ask anyone to trust a mechanism we have not inspected.”
Halden Rusk
Ally, retired surveyor and keeper of the gate ledger
WantsMake sure the party understands the old flow marks and gets the ledger out of the flooded records station intact.
“These marks are not decoration. They show where the water wants to go when the stone starts arguing.”
Ilyra Senn
Witness, Kelpstrand salvage worker who escaped the lower works
WantsProtect the gate chamber and its creatures while helping the party remove the unfamiliar device.
“That cold little thing is biting the water. Get it off, and perhaps the old one will stop blaming everything that moves.”
Old Kettle
Wildcard, ancient basalt-plated beast
WantsDefend its warm nesting shelf and drive away loud, threatening intruders. It is distressed by the chilling water, not malicious.
“Grrrraah. The water. Mine.”
How it ends
Rewards
Items
Station 4 maintenance tools, useful for freeing the gate chains with a DC 12 Dexterity (Sleight of Hand) check
Halden's water-resistant survey ledger, which lowers the safe-flow marks check to DC 11
The rime-grey fitting, if removed; it is a mysterious, nonmagical-looking object whose properties and maker are not identified by this adventure
On a win
When the final required task is complete and Pressure is 2 or lower, the gate settles into its frame.
The knocking fades, chains stop trembling, and the warm current resumes an even course through the channels. If the fitting was removed, its black ice does not melt in the chamber air. If Old Kettle was calmed or the cause was fixed, it returns to the warm shelf and watches the party leave.
What it leaves open
If it fails
- The party does not remove the fitting, clear the weep-holes, free the chains, and reduce Pressure to 2 or lower before three Cracks accumulate.
- If the gate takes three Cracks, the slab shifts and the chamber begins to flood. The party must escape up the ladder; Kelpstrand's current becomes unreliable and the settlement begins emergency rationing of heat. The gate can remain a future repair problem rather than becoming an instant total loss.
- The characters abandon or mishandle the approach to the records station.
- The record station is damaged or its ledger is lost. Halden cannot provide the safe-flow guidance, so the party must rely on their own observations and make the relevant Investigation check at DC 13 rather than DC 11.
- The party attacks Old Kettle or repeatedly approaches its nest without calming it or addressing the cold water.
- Old Kettle drives the party away from its shelf or injures a character, but it remains in the cavern. Retreat is possible; returning with food, a calmer approach, or a plan to remove the fitting can change its response.
Complications (d6)
- 1A warm-water eddy spins loose equipment toward the channel. A character can catch it with a DC 12 Strength (Athletics) check; on a failure, a tool or unsecured object is swept 20 feet away.
- 2Mineral crust collapses over one approach marker. Until a character clears it with a successful DC 12 Strength (Athletics) check, the next character navigating that stretch has disadvantage on the check.
- 3A burst of steam obscures the walkway for a round. Creatures moving more than 10 feet through it must succeed on a DC 12 Dexterity saving throw or fall prone.
- 4A sharp pulse makes the water slap against the stone. One creature working at the gate must succeed on a DC 12 Strength saving throw or lose its grip, ending its current interaction with the winch, fitting, or weep-hole.
- 5A ratcheting chain catches on the winch. The next attempt to free the chains requires a character to first spend an action releasing the snag, or the check is made with disadvantage.
- 6Old Kettle gives a low, distressed bellow from the warm shelf. Until someone offers food, calms it, or removes the fitting, the next character to approach within 10 feet of its shelf draws its attention.
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