From publisher blurb:
A group of Ragnar cultists have found a magical relic, a chalice that can never be filled, and are using it to lure treasure hunters and adventurers to their lair. Foolish adventurers who take the bait and come to the lair are hunted by the monsters guarding the chalice, and are then sacrificed to Ragnar. Leftover bodies are then given to the wyvern lurking in the cavern’s depths.
The cultists believe that Ragnar watches over them through the wyvern’s eyes, and any blood poured into the chalice as an offering increases his magical power. Eventually, they plan to sacrifice the monsters they’ve paid and blackmailed into being guards - ogres, bugbears and cromags.
The chalice is a magical artifact - when liquid is poured into it, it vanishes. If the command word is spoken while tipping the chalice, any stored liquid pours freely out of it. Unfortunately, it’s currently full of blood, and nobody knows the command word.