LFS: Ritual sacrifice in a clearing in the park - hero observes

[Dark_Raven]

Hi all. Not even sure if this was a story on Lit, or a published novel... The only part I can recall is that the protagonist is (jogging?) in a park, then for whatever reason goes off into the woods and climbs a tree to observe a circle of hooded figures performing a ritual sacrifice on a full moon? IIRC, this ritual allowed them all to transform and become younger? As the protagonist tries to escape, he's chased by someone, perhaps a warewolf. I'm not certain, but being in close proximity to the ritual may have given him powers.

I believe he may have seen the robed figures carrying torches... Thanks!