I've been able to decipher what those Wastewander bandits have been doing. It looks like they've found an ancient summoning spell and have restored it. I knew they were up to something good. The message you brought mentions that they are planning to summon this demon tonight. Go to the ritual site at the Wastewander camps to the west and perform the summoning before they can. Slay the demon. I will sense the moment that its essence dissipates and revel in it.