Free D&D One-Shot · Level 5 · 5e Compatible
Free Level 5 D&D One-Shot: The Drowned Cartographer
A complete 3–4 hour D&D one-shot for 4–5 level 5 characters
Need a free D&D one-shot for a mid-level party that feels complete, not improvised? The Drowned Cartographer is a printable, ready-to-run 5e adventure for 4–5 level 5 characters, built for a 3–4 hour session with no prep beyond reading the page. It gives you a nautical mystery, ghost-ship investigation, cosmic-horror finale, four structured scenes, quick NPC stat blocks, a d20 harbor encounter table, rewards, and an ending hook. Use it when your table wants a polished one-shot tonight and you need the clues, encounters, and DM notes already organized. It also doubles as a printable backup adventure for convention slots, travel sessions, or weeknights when prep time disappears.
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The Hook
Three months ago, master cartographer Aldric Fosse drowned when his survey boat capsized in perfectly calm water. Last week, his ghost appeared at the Harbor Chart tavern and erased every map on the walls with a wet hand. Since then, no captain will leave port — the sea charts feel wrong, as if redrawn by something that doesn't understand coasts.
The party finds a rolled map washed up on the docks, covered in uncharted routes with a message scratched into the margin: 'DO NOT SAIL WHERE THIS POINTS. I ALREADY DID. — Aldric Fosse.' The harbor master offers 500 gp to anyone who can stop the ghost before trade dies entirely. But the map points at a place no sea chart shows. And the tide has started going out four hours early.
GM brief: Run this as nautical mystery with cosmic horror undertones. Every strange detail should feel like a symptom of something watching from below. The players can survive this without fully understanding it — and that's fine. The sea itself is wrong here.
Scene 1 — The Tide Chart Tavern
Goal: Meet Aldric's ghost, learn what happened, and acquire the map key before the next tide.
- Aldric's ghost appears wet and frantic, erasing charts as it moves — not in malice but in panic, trying to prevent anyone from finding what he found.
- Captain Sura Vane admits she loaned Aldric the boat and feels responsible for whatever followed him back.
- The ghost can communicate in writing if given chalk and a dry surface; it reveals it found a place called 'The Pale Shelf' and something there taught itself to follow him home.
Challenge: DC 15 Arcana or Investigation to decode Aldric's damaged log tucked behind the bar, revealing the island's name in an old naval cipher and its approximate bearing. Without this check, the party can still sail by following the ghost.
Scene 2 — Aldric's Lament (The Ghost Ship)
Goal: Board Aldric's recovered survey boat, now sailing itself, and find the hidden notes below deck.
- The ship sails in complete silence and navigates independently toward The Pale Shelf; its compass needle points down instead of north.
- Below deck, Aldric's last charts are still pinned to the board — one shows a deep-sea vent with a sketch of an eye at its center.
- The ghost appears here again, fully coherent: it asks the party to destroy what it found, or let it pass on knowing the entity below will stay.
Challenge: DC 15 Perception to notice the hull barnacles are arranged in a pattern of eyes. When noticed, DC 13 Wisdom save or take 2d8 psychic damage as something notices you noticing. Success means the entity doesn't get to act in the first round of Scene 4.
Scene 3 — The Pale Shelf
Goal: Investigate the impossible island and learn the full truth before the entity surfaces.
- The island is a low shelf of pale rock that shouldn't be visible from the surface — only Aldric's map shows it, and standing on it feels like standing on something alive.
- The rock is carved with tide-marks in a language adjacent to Primordial, recording depth measurements going down ten miles straight.
- Aldric's original survey notes are here in a waterproof case; the last entry reads: 'It saw me looking. I think it has been waiting for something to look.'
Challenge: DC 15 Nature or Arcana to understand the tide-marks: the island is the top of something very large that has been rising by half an inch each year. DC 13 History reveals this matches three ancient port disasters in the last 400 years.
Scene 4 — The Depth-Warden's Bargain
Goal: Defeat or negotiate with the ancient entity before it fully surfaces.
- The Depth-Warden surfaces as a mass of luminescent deep-sea flesh and grinding glass teeth, speaking in translated tide-patterns.
- It claims it was mapping the surface the same way Aldric was mapping the depths — it considers this a fair exchange and wants Aldric's ghost as 'its cartographer.'
- A third path exists: returning the tide-mark stones from The Pale Shelf to the vent as 'unread data' convinces the Depth-Warden that nothing mapped it and it has no claim.
Challenge: Combat option: Defeat the Depth-Warden (AC 14, HP 105). Negotiation option: Three DC 16 skill checks using any applicable skill — each success reduces its power; each failure triggers a Depth Pulse (4d8 cold + 4d8 psychic, DC 14 Con half). The 'unread data' option requires DC 14 Arcana plus the tide-mark stones.
Captain Sura Vane
Seasoned smuggler-captain, guilty conscience, fast ship
AC 15 (studded leather), HP 52, Speed 30 ft., Passive Perception 15
STR 13, DEX 16, CON 14, INT 14, WIS 14, CHA 15
Traits
- Sea Legs: Advantage on all checks and saves made aboard a ship or in the water.
- Guilty Navigator: Will sail the party to The Pale Shelf if they succeed on a DC 13 Persuasion check or show her evidence the trip is survivable. Failure means she needs a second convincing attempt.
Actions
- Cutlass: +6 to hit, 1d6+4 slashing damage.
- Flintlock Pistol (1/encounter): +5 to hit, range 30/90 ft., 1d10+3 piercing damage.
Ghost of Aldric Fosse
Terrified spirit trying to prevent what he caused
AC 11, HP 32, Speed 0 ft., fly 40 ft. (hover), Passive Perception 14
STR 7, DEX 13, CON —, INT 17, WIS 14, CHA 12
Traits
- Cartographer's Eye: Aldric can describe any location he has ever mapped with perfect accuracy, including hidden passages or exits. He mapped every inch of The Pale Shelf.
- Haunted Knowledge: Once per scene, if players ask the right question, Aldric can reveal one non-obvious fact about the Depth-Warden — its weakness, its bargain, or its claim.
Actions
- Erasing Touch: +3 to hit, 2d6 psychic damage; on a hit, the target forgets one memorized spell slot (recovered after a long rest).
The Depth-Warden
Ancient ocean entity, curious and implacable — not evil, just old
AC 14 (natural armor), HP 105, Speed 0 ft., swim 60 ft., Passive Perception 16
STR 20, DEX 10, CON 18, INT 16, WIS 15, CHA 14
Traits
- Tidal Form: At the start of each of the Depth-Warden's turns, creatures within 20 ft. must succeed on DC 14 Strength save or be pushed 10 ft. away.
- Deep Sight: The Depth-Warden can see through any creature that has looked at it directly, granting advantage on attack rolls against that creature.
Actions
- Crushing Pressure: +8 to hit, 3d8+5 bludgeoning; target is restrained until end of their next turn.
- Depth Pulse (Recharge 5–6): 30-ft. cone, DC 14 Constitution save or take 4d8 cold + 4d8 psychic damage, half on success.
d20 Harbor Encounter Table
Roll at the start of Scene 1 or whenever the atmosphere needs texture. Each entry is a rumor, omen, or detail the party can investigate.
- A fisherman keeps pulling up boots with feet still in them but refuses to stop fishing.
- The tide has come in four hours early twice this week, flooding the lower market.
- All charts in the harbor master's office were erased overnight and replaced with diagrams of ocean trenches.
- A pilot claims his compass has been pointing down instead of north since Tuesday.
- Three sailors swear the ocean was perfectly flat — no waves — the night Aldric's ghost appeared.
- A seal on the dock has been staring at the harbor entrance for six days without moving.
- Sailors report a ship moored two leagues out that isn't in the register and shows no lights.
- The dockmaster's ledger has an entry for a ship named 'Pale Shelf' registered to A. Fosse, but no one remembers it.
- Someone has been leaving gifts of rope and dried fish at the slip where Aldric's boat was kept.
- A net came up full of glass bottles containing rolled maps of places no one recognizes.
- Two different merchants received the same unmarked letter: just a sketch of an eye and a depth measurement.
- A fog bank sits exactly two miles out and hasn't moved in three days.
- The harbor bell rang from underwater; the sound was heard on three docks simultaneously.
- A drunken sailor sketches perfect maps of the ocean floor in spilled beer, then can't remember drawing them.
- Three ships left port without crews during the night and returned at dawn with holds full of salt.
- A lighthouse keeper claims the light turns blue on nights when the ghost walks.
- Someone has been painting eyes on the bottoms of every boat in the harbor.
- The harbor cat was found atop the anchor chain, perfectly still, watching the water.
- A long-dead navigator's ghost was seen arguing with Aldric's ghost over a chart no one could read.
- The sea smells like copper and ozone exactly one hour before the ghost appears.
Rewards
- Aldric's Binding Compass: A masterwork compass that always points toward the nearest sealed rift between planes. Once per day, the attuned bearer can ask for a bearing to a specific destination as if casting Locate Object at 4th level.
- 500 gp from the harbor master, plus 200 gp bonus from Captain Vane if the party saves her ship and her reputation.
- The Pale Shelf Charts: Aldric's complete survey notes, worth 2,000 gp to the right collector (archmages, the cartographers' guild, or a navy). Contains ocean features no other map records.
Ending Hook
The Depth-Warden's departure opens a crack in the ocean floor that closes within minutes — but not before something small and glass-bright drifts up through it. It looks like a compass rose carved from ice and it points the same direction every eye on the docks turns: inland, toward a mountain range that was never named on any map. Aldric's ghost, finally free to pass on, turns toward it one last time before dissolving. His last whispered word is a cartographer's notation: 'Here be something worse.'
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New complete D&D adventure delivered to your inbox every week. Scenes, NPCs, encounters, rewards — run it the same night.