You come to a large stone altar. Flakes of dried blood and bits of hair crust its surface. Underneath, a cobweb of deep gashes in the stone are testimony to the sacrifices that have occurred. The space before the altar is smooth from centuries of use. Water dripping from above has created a patch of mud behind the altar.
Searching the area around the altar (an automated Survival 17 check against the party member with the highest survival skill) reveals a battered, Waterlogged Journal in the mud.
This marks the abrupt end of the scripted interaction, however - though it is mostly illegible - reading the journal hints at the familiar name of one Arkemyr, as well as something called "The Sanguine Harvest". There's not much you can immediately do with this information, but if you head back to Periki's Overlook in Neketaka you can ask Arkemyr about it at his manor.
When asked about The Sanguine Harvest, he will mention that an explorer named Ceulia made a similar inquiry a number of seasons ago, and that there may be a book - The Cult of the Sanguine Harvest - relating to it in the basement. If you already looted his basement in The Archmage's Vault, it's likely you already picked it up. The book describes The Sanguine Harvest as a mysterious cult. On the 16th of every month, they choose a captive to be scarified on their altar to fampyrs to empower a soul-draining great sword.
Head back to the island and wait until the 16th before approaching Bent Bough Forest again. This time, a group of kith dressed in red robes surround the altar, performing some sort of ritual. You can choose to observe the ritual, which plays out exactly as the book describes, or attack the cultists at any point during.
If you observe the ritual all the way through, a Stealth 13 check on your entire party will determine if you can hide from them when they leave.
If you are spotted, or attack the cultists after their sacrifice, this puts you in the Forest staging area, against a number of cult members including the Grand Harvester himself. Killing them nets you a bunch of Superb quality gear, and the unique Sanguine Great Sword.
If you choose to attack the cultists before they sacrifice their victim, Winking Audr joins you in combat (although you should be careful since she dies fairly easily). Kill the cultists and speak to Audr to get the option to recruit her as a crew member. Unfortunately this way you won't be able to get the great sword.
During the ritual, a wizard with the spell Arkemyr's Dazzling Lights, or a priest with Holy Radiance can blind the fampyrs with dazzling light. This sends the fampyr's scattering, but one of the cultists draws the great sword from the altar and begins to approach you. Depending on when you did this during the ritual will determine if you can either save Winking Audr or get the sword. However currently it ends the interaction with no outcome (this is likely a bug, since by the text we expect to enter combat - perhaps with a reduced amount of enemies, and the possibility of both saving Audr and obtaining the sword).
You don't need to collect the journal or head to Arkemyr in order to trigger the event, the only requirement is that it be the 16th day of the month when you enter the interaction.
Usage of the priest spell seems to be unavailable, even if a character has it. There may be another requirement, or it might just be broken.
If you leave the interaction without "completing" it you can come back at a future 16th of the month.
Killing the fampyrs in Fampyr's Crypt does not affect this interaction.
The connection between The Sanguine Harvest and Arkemyr is the explorer Ceulia, who is likely the author of the journal you found. Having visited Arkemyr to ask if he knew of it, perhaps she then ventured to the altar only to be captured and killed by the cult. Another possibility is that Audr is Ceulia, who joined the cult long ago.
The Rogue Trickster's Arkemyr's Dazzling Lights cannot be used in place to blind the fampyrs (it is limited to the Wizard spell).
Scripted interaction graphics
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