Moderators of the wildly popular VORPG, Polyworld, had no idea that one of their most famous cites Edotown had been stolen and for quite some time. No wonder there were so many complaints and bug reports coming in.
The PCs find a strange helmet, when donned it will take control of that PC and speak and act trough him/her. It explains that it is benevolent and needs their help in a quest and that it will stop possessing the PC when the task is done. Great if a player is gone for a number of sessions.