Hey everyone, this is my first post to let me know if I'm doing something wrong.

Here's a litttle background: My campaign started off with a very loose idea, to investigate heresy in a small trading settlement on an agri-world. I am playing with some first time acolytes, and so I wanted to allow them to shape the story as much as possible. To allow for this, I wrote up a couple vague directions I wanted to take the campaign in, and decided to improv the story a bit based on where they seemed to be going. They ended up at the darkest of my possible outcomes, a daemonic ritual that they interrupt, causing a warp anomaly that floods the planet with daemons.

Now, I have a sort of set end goal for this campaign, and that is to fight their way to the source of the anomaly, and then preform an exorcism to close this. One of the acolytes is a psyker, so I feel like that would flow well.

The issue I'm having is that I don't know how I would do this. How would you handle this?

Exorcism is an antique ritual, generally performed by clerics and not psykers. They are more of rites dans resonate into the warp and bannish daemons from hosts, than psychic powers.

I once developped a ritual which needed 3 steps:

-Performing the basic rites (circle of salt, positionning religious items, etc.) which required a test of scholastic lore (occult) -20. To perform the exorcism, they needed specific items (an encenser from a holy figure, blessed candles, holy water, etc.).

-Then, having contact with the daemon: you bring him in the ritual circle, this part is where the exorcist establish contact to bann the daemon. It's an opposed willpower test with the daemon. This determines the time the exorcism will take place. An exorcisme takes 1D5 hours +1 by degree of failure of the exorcist in the test.

-Exorcising: It's a scholastic lore (imperial creed)-10 against the willpower of the daemon. It must be perform once for each hour of the ritual.

If the basic rites are a failure, the test becomes -30 instead of -10.

You decide how many level of success it takes in the cumulative tests to win, and how many of failures it takes to fail catastrophically.

The longer the ritual, the more tests you do, but it can also has its own complications: the daemons destroy the ritual, minions come to his help, etc.