"Before I met Barnes, while studying natural science, I learned about what you might call 'magic'. It's not so much of sorcery as you might think in fairy tales, but more of a deeper understanding of how the world actually works. It's something I feel I could spend my entire life studying and never fully understand; rather, I'd still barely understand it. Barnes knew far more than me, but he and I were on the same page about these issues.
I went with the other two constables to where that monster was that attacked Barnes and I saw it. It is monstrously huge, and I do not think all of the men and muskets in this town could kill it, or if we could, it would come at a prohibitively high cost. I do know a bit of banishing such creatures back to the realm where they came, but I need two other people for the ritual, and it cannot be interrupted. The ritual will bring the creature here, but physically bind it. I'd like the other two constables to guard us while we do this, to make sure that we do not stop. Are you willing and able to help? You need to be able to maintain your focus no matter what you see, knowing that this should save a great many lives."
Bhu: does it matter who the other two people in the ritual are? My thought was to have them help with the ritual, leaving the other two PCs (who are hopefully more skilled) to guard us.