Critical Role Vox Machina Origins I #2

Scanlan and Grog loot a shark-man temple in the swamp outside Stilben, where they uncover priceless treasure and one strange artifact-a glowing vial of liquid. Returning to the city to determine its use, they're almost killed by assassins and then almost arrested by the Watch! Just when they think they're in the clear, they're approached by an incredibly pompous magic user who threatens them if they don't give up the vial. What's in this flask that's so important?