“ A casual remark by one of the party about something met on a previous adventure leads to a summons to and grilling by the Mages' Guild (or equivalent), probably resulting in an expedition back to that area to recover the things for study by the Guild. The party's presence will be 'requested' for this expedition.”
“ During a public holiday in the small town of Wyrmbersch, the Mayor is accidentally killed by a statue which falls from the roof of the Town Hall. As shocked spectators crowd around the body, they discover that the Mayor, at the moment of death, shape-shifted into a squat, stunted humanoid figure, it's grey skin dominated by bony ridges and lumps. How long was the Mayor an imposter? And who else in the town isn't what they seem to be?”
“ The PCs are accosted in a major city containing at least one famous fortuneteller / prophet of the future. They are informed that their as-yet-unborn child will (insert terrible evil), and that, although they are very sorry, the PC must be executed to keep this from happening.”