Help me model a "Planar Hunt" ritual

[DocBadwrench]

As a part of the overall story within my campaign, my characters are about to gain the services of someone who can hunt for planar creatures. The idea is that they tell this person everything they know about him, and the NPC is able to get them closer to their quarry.

I want to be able to model this ability with the following things in mind:

• It should have a cost, in materials, that is enough so that they can't do it all the time, but not so much that it's prohibitive.
• It should guide them toward their quarry, but still allow for enough flexibility to hook them into sub-adventures that lead to still more knowledge.
• The person they are following is (initially) not aware they are searching for him.
• The person they are following is also moving about the region on his own agenda.

I'm wondering if, say, the players get this NPC to do it once and it leads them somewhere this person has been before. After going there and taking part in combat/non-combat encounters, they gain some evidence of his passing. This would make the subsequent search get closer to the person in question.

While the NPC will be able to render assistance that gets them started, I want to be able to turn something like this into a ritual that one or more of the player characters can perform on their own.

I like the idea that they could, perhaps, see behind the eyes of the person, or that they could accidentally locate another planar they were previously unaware of. Basically, any result that could get them closer to their quarry or a cool-side quest (while obviously that means the ritual was less than successful, they could benefit by making a friend thanks to the error).

I think you can tell what I mean. Let me know what you think and thanks in advance to any of you who wish to help.

Warmest regards,
DocBadwrench

 

[DocBadwrench]

Bumping in the hopes of grabbing your attention.