Summary: A Chaos cult in the town is attempting a ritual to summon a herald of each of the four Chaos Gods in turn. Once the ritual is complete, the four heralds shall meet in the town square to do battle for supremacy over the town while the whole thing is sucked into the Warp. This would be bad for the economy.
Discovery: The town is hosting a festival as the characters arrive. They’re invited to stay during the festivities. Fair food is sold at extortionate prices, but it’s a taste you can’t find any other time of year. Performances of all kinds are put on, of clever outlaws outwitting brutish Arbites, and of Chaos gods – far more than the normal four – getting up to shenanigans with one another, and the occasional morality play exalting some virtue or another.
A great fire daemon who stole the light from the Emperor and gave it to mankind so they could see the truth for themselves. Daemons of sea and earth whose champions fought each other for a century, passing the feud on to their children until finally both clans were exterminated, and yet both became the most exalted of their patrons’ host in the Warp. A foolish thief who breaks into a sorcerer’s shrine looking for a wand that grants wishes, stumbles across a Chaos artifact that makes the walls weep blood, and then looks for something that will fix the first artifact, and each one fixes the problem caused by the last artifact but causes another even worse, until finally the sorcerer arrives to solve everything and turns the thief into a rat which he keeps as a pet.
Exploration: There’s also games of skill, which give out small prizes. One game has players standing at a line a dozen yards from a series of concentric rings on the ground and trying to throw beanbags into the center ring, a Challenging(+0) Ballistic Skill test. Another is an obstacle course, a Hard(-20) Athletics test. Yet another is a high striker, requiring the player to strike a button with a hammer, and the harder the button is smashed the higher a metal slug is pushed up a meter, the goal being to get the slug to hit the bell at the top. This is a Challenging(+0) Strength test. The cost of entry to each of these tests is an Abudnant(+30) Influence check, and for basic success offers a prize which is a small trinket with some (completely non-magical) Chaos theme whose only mechanical use is that it is also of Abundant(+30) value, and can be traded. With three degrees of success, a similar trinket can be won that has a value of Plentiful(+20), and with five, an ornately crafted trinket with a value of Common(+10), made with good craftsmanship, though simple material.
Several of the games are less family friendly. A gladiator pit where townspeople are dropped in with two alternating events, one where each gladiator is given a knife and then their off-hands are tied together and one where two gladiators are put into the arena with just one knife. A large tent hosts a drug-fueled orgy. Some of the food tastes vile, and a Challenging(+0) Medicae check will diagnose (and cure) the disease that will otherwise cause 1d5 permanent Toughness damage, unless the eater is a Nurgle cultist, in which case they are immune.
Throughout the night, cultists running the different events are kidnapping one another and imprisoning their captives in large wickermen. Late at night, at the witching hour, the wickermen are rolled out into the center of the town. Each of the five wickermen is lit on fire one by one. One for Khorne, one for Slaanesh, one for Nurgle, one for Tzeentch, and one for Chaos Undivided, each stuffed with cultists of their rivals, from sorcerers who’ve been drugged into unconsciousness to prevent them from using their powers to escape to brutes in security who’ve been bound tight to regular carnival-goers who’ve pledged allegiance to one cover cult or another for each of the five factions to children who end up in the cult because that’s where their parents are.
Confrontation: As each wickerman is lit on fire, a herald of each of the Four Gods is summoned in turn, and then finally a Chaos Fury for Chaos Undivided. When all five arrive, they battle to the death. When only one herald remains in the center of town, the entire town is sucked into the Warp.
Any effort to disrupt the festivities will be met with the local PDF squad rolling out to stop them in their chimera. This town has lots of nominal Imperium institutions left over, but it’s deep in Chaos territory and everyone is a part of the cult. The PDF are split between Khorne and Slaanesh, and if one or more party members are incapacitated during a fight with the PDF, and anyone not incapacitated flees or surrenders, the PDF will fight with one another, ultimately physically, to determine whose wickerman the defeated party members will end up in. Characters will be bound tight, requiring a Difficult(-10) Strength test or a Challenging(+0) Acrobatics check to wriggle out of the restraints.
If the characters avoid defeat and/or capture and are able to successfully destroy at least one wickerman or liberate all of the captives within it before the ritual begins, the ritual will be disrupted. If there’s at least a few hours before the witching hour, cultists of the snubbed herald will hastily attempt to assemble a new wickerman. All they need is wicker, which they have plenty of left over in their workshops and homes. Outside the festival area things are quiet and dark, the town having poured all its inhabitants into the brightly lit heart. If the characters foil this effort, too, or if there are only one or two hours left before the witching hour (not enough time to assemble a new wickerman), the snubbed herald will be summoned, but he will devour his own followers and refuse to contribute his daemonic energy to the ritual, thus making it impossible to drag the town into the Warp. Instead, the herald will slaughter as many of his own cultists as possible and try to drag his cult’s leaders into the Warp with him to punish them for their failure. Upon realizing that the ritual will not be completed, the other heralds will do the same.
If the heralds are all successfully summoned and placated with a proper human sacrifice in the wickermen, they will begin their battle for the town. If the battle between the five heralds is interrupted, all the remaining festival-goers, an effectively endless number of cultists (several hundred in all), will join in the melee to support their chosen daemon, but they’ll fight each other as much as the characters or their rival heralds, so only a few cultists for each daemon need be actually rolled for on the battlefield. Once only one herald is left, the surviving herald will take a full action to use the ritual energies of the festivities to drag the whole town into the Warp. The only way to prevent this from happening at this stage is to kill the herald before their turn comes up and they take their full action.
Any cult leaders who are able to escape the wrath of an angered herald until either the end of the witching hour or until the herald is slain will attempt either to flee or to seek revenge on the characters, depending on whether they have a good chance of successfully capturing or at least killing the characters if they go for that second option.
Reward: If the characters fail to stop the ritual, they will end up shifted through the Warp into Chaos Landing, from whence they can make their way back to the Materium. The loss of the town on the river will drastically harm the economy and cause a -5 penalty to all requisition tests along the river and -10 to all requisition tests in any other town. The economy will adjust to the loss of the town over time, the penalty going down by 1 every 1d10 days. After 5d10 days, the penalty on the river will be gone, and after 10d10, the penalty will be gone all over.
If the ritual is prevented, then one way or another the entire cult leadership has probably been killed or fled town or been abducted into the Warp. The characters can install a new ruler at-will. Whoever takes over the town gains 1d10 Influence and anyone who knows them gains 1d5. The town can additionally be levied at a cost of 2 Influence points in order to automatically succeed at an Influence roll for goods or services from the town. The town can provide anything that’s common or cheaper, any solid projectile weapon or service that’s average or cheaper, and any medical care, low-tech weapon, or armour that’s scarce or cheaper.