Celestial - Hound Archon:
The setup: The city has seen a large increase in the number of lycanthropes within the city walls. The PC's goal is to eliminate the threat of the shapechangers.
The specific encounter: There is an attack by werewolves (and others, like were-dogs, were-hyenas, etc...) on a large gathering of the inhabitants of the city. This could be a fair, parade, market-place, anything. During the attack, the city's mage guild summons several Hound Archons to combat the lycanthropes. The Hound Archons are fighting in canine form when the PC's get to the scene of the attack. (or, a group of Hound Archons themselves decide to get involved.
Not only does the party have to fight lycanthropes, they have to do so without injuring the civilians left in the area, and they have to move quickly to stop more people from being killed/infected in the attack. Bad thing is, they may inadvertently attack the Hound Archons, not knowing who/what they are; the Hounds would probably react badly to being attacked by these newcomers, not knowing which side the PC's are on. This presents the possibility of a three-way melee between the Hound Archons, the PC's, and the Werewolves.
Next: Celestial - Avoral.