Long ago the druid Aelwen Tarr sealed her staff and her notes on the chuuls in a stone box in the last pillar at the far end of the causeway. She did it to keep them from another druid who wanted to use the chuuls against Naath. He hunted her into Whispermire Holt, and she drowned there. She is now the Banshee of the holt. The chuuls still guard the water on her old orders. They attack anyone who steps off the stones and never chase anyone who stays on them.
The singing comes from the Lost Ones, ghosts of elves who drowned on the causeway. This morning they have caught someone. A young elf reed buyer from Naath (Commoner) slept on Hessa's porch last night. At first light he walked out onto the stones toward the song. He is charmed, past the first gap, walking slowly toward the second. He stops often to listen. The Lost Ones fade back into the mist when they are hurt below half, or when the mist lifts at about 10:00.
Hessa Marle wants to be left alone, and she wants her grandmother's knowledge of the marsh remembered. Her grandmother's charts show a second way across, through the reeds. She sells a look at them for a fair price, or gives it free to anyone who goes after the reed buyer.
The Banshee of Whispermire Holt, the ghost of Aelwen Tarr, wants her cache kept out of the wrong hands. She talks only to those who come with weapons sheathed.
Virelien Moraeth, head scribe of The Cloister Archive, posted the notice. She pays for the druid's notes.
Budgets for one level 3 character are Low 150, Moderate 225 and High 400 XP. Add the same row for each other level 3 character present. The Murkveil Crossing is Deadly (9+) for Encounter Checks. The Chuul (1,100 XP), the Lost One (700 XP each), the Shadow Grasp (1,800 XP) and the Banshee (1,100 XP) are all far over budget and over the CR ceiling. Run them as dangers to get past, never as fights to win.
The water. A creature who falls in has one round to climb back onto the stones. That takes a DC 12 Strength (Athletics) check, or no roll with a rope from someone on the stones. A creature still in the water at the start of the next round is attacked by 1 Chuul, which grapples and pulls it under. The chuul lets go of anyone who gets free and back onto the stones.
The empty blanket. The Murkveil Crossing, 0001-04-12, 07:00. Right after the opening, Hessa sees the reed buyer's blanket empty on her porch. Wet boot prints lead onto the causeway. A DC 12 Wisdom (Perception) check spots his shape in the mist past the first gap. He reaches the second gap at about 07:15 and steps off at 07:20 unless someone holds him.
The first gap. It can be jumped with a DC 10 Strength (Athletics) check. A failure means a fall into the water. The reed buyer cannot be talked out of the charm. He must be held, which takes a grapple, or knocked out.
The second gap and the singers. 2 Lost One stand on the stones just past the second gap, singing. Each round, everyone within 30 feet of them makes a DC 15 Wisdom saving throw or is drawn 15 feet toward the nearest edge. Anyone drawn past the edge falls in. A Lost One can also try a Charm Glance (DC 14 Wisdom saving throw). Backing out of range ends the pull. The fallen post under the water holds anyone who goes slowly. That takes a DC 12 Dexterity (Acrobatics) check, and a failure means a fall.
The keystone and the third gap. The old carving on the keystone shows an oak leaf over still water. A DC 13 Intelligence (History) check names it as a druid's warning to turn back. The Shadow Grasp lives in the water under the third gap. It grabs at anyone who crosses there and pulls them in. Steer the players toward the reeds or toward Aelwen.
The reed path. Hessa's charts show old hummocks through the reeds that go around the third gap. Following them takes three DC 13 Wisdom (Survival) checks, one for each stretch. Each failure is a step into the water. Halfway along, 1 Giant Toad waits in the reeds (200 XP, Moderate for one character). For two characters use 2 Giant Toad (400 XP, Moderate for two). It flees when hurt.
The druid's ghost. Whispermire Holt, one hour west. The Banshee calls travelers by name and leads them in circles. Staying on course takes a DC 13 Wisdom (Survival) check, and a failure costs an hour. A Will-o'-Wisp drifts over the pools and tries to lead people off the path. If someone promises to keep the cache out of the wrong hands, Aelwen tells them which stone to pull so the box opens cleanly, and she tells how she died. If she is attacked, she wails. Every creature within 30 feet makes a DC 13 Constitution saving throw or drops to 0 hit points.
The cache. The far end of the causeway. The stone box is sealed into the last pillar. With Aelwen's word it opens with no roll. Forcing it takes a DC 15 Strength (Athletics) check, and a failure cracks the box and soaks half the notes. Inside are her staff (a Druidic Focus) and her notes. The notes tell how she brought the chuuls and how a druid could send them away.
0001-04-12, 07:20. The reed buyer steps off the second gap, and a chuul takes him.
0001-04-12, 10:00. The mist lifts, and the singing stops.
0001-04-13, 22:00. The singing comes back, with one more voice.
0001-04-15, 09:00. A Seeker crew of two from Naath (2 Scout) comes for the cache notice and goes past the keystone.
0001-04-15, 18:00. One of them comes back alone and does not speak.
0001-04-16. Hessa walks to The Wyrm Bones to tell Oswin Farrow, and stops giving advice to travelers.
Good. The reed buyer lives, and the notes reach Virelien Moraeth whole. Aelwen's promise is kept.
Mixed. The notes reach the archive, but the reed buyer drowned or half the notes were soaked.
Bad. Someone is lost in the water, and the cache stays shut.
50 gp from Drakha Mol-Urn at The Seekers' Hall for the notes, as Virelien's notice promised. Virelien adds 20 gp for the story of how Aelwen Tarr died.
Aelwen's Druidic Focus is the players' to keep if Aelwen agrees.
Virelien offers the Archive Copyist job to anyone who can read the old hand.
Hessa Marle becomes a friend and offers her porch in bad weather. The reed buyer's family in Naath owes a favor.
Heroic Inspiration for bringing the reed buyer back alive.
Sending the chuuls away. The notes need a druid. Haren Gullis at Haren's Farmhouse or Tharivol Dennistein at the Eastern Eldertree Gateway could try.
The names of the drowned. Virelien Moraeth can find the names of travelers lost on the causeway, so they can be read at The Stone of Names in winter.
The Shadow Grasp. It still waits under the third gap and slips into the dreams of anyone who sleeps near it.