The quest NPC managed to get a hold of one of Sotha Sil's time-keeping devices (wayward Temple member, unlucky Thieves Guild toady, Archaelogical Society stumbling over a fragment of Clockwork City?). They've messed with it to the point they were able to turn back time for an hour, but with the result they are now stuck in a time loop, reliving the same hour over and over again.
Might need a quest chain, but a few different ideas:
--the NPC asks to be escorted somewhere for some reason, but keeps teleporting back five steps (evil)
--player keeps talking to the NPC who keeps forgetting them. player can play around with various options (killing the NPC, playing pranks on them, trying to convince them to give up the artifact), etc, which all fail, until (perhaps) the player has to do the above escort to leave the area of effect of the time-keeping device.
--a nearby vampire wants to kidnap the NPC to have a neverending supply of blood, and tricks the player into doing so. However, when the vampire tries to use the NPC in this fashion, weird things happen.
--take the NPC out to have the time of his/her life in the nearby town, doing things like kissing their married teenage sweetheart, sassing the local lord, stealing everything from a wealthy noble and then dumping it in the canal, etc. The player helps the NPC do each of this escapades in various ways. The NPC thinks all these things will have no consequences as time keeps resetting for him/her, but this is not precisely the case. After the player bids the NPC goodbye, if they go around talking to all the other NPCs they notice things happening like the sweetheart being pregnant and not being certain how, the local lord is having a bad day and for no reason at all sacked his best secretary, the wealthy noble went broke and moved out of town, etc. The player could perhaps report these happenings to a guard, who'd look confused, or to the Temple, who send out Ordinators to apprehend the device.