Somebody in distress; bandits are going to do nasty things to him/her. Once saved (if ever): he is going to introduce the party to the next adventure or to an interesting subplot of whatever the current plot is, or just possesses the clues to maybe successfully complete the present plot.
Alternative: he/she is very evil. Once saved, he/she invites the party to his castle and makes disappear the party members one by one... a la Agatha Christie... because he wants make a human sacrifice with them... Be sure to have a NPC disappear early and reappear in due time to save the group, if they are unable to get out of this by themselves. I used this plot, the group liked it but I needed a Deus ex Machina In this plot the guy in distress must look nice and not dangerous at all.