[adding to the "kidnapping"-idea suggested by Huicton and a who-done-it-twist suggested by Aynara]

"how about stealing something like a codex incorporating the who done it theme and the Carpenters cup clues and object burial at peoples' homesites across all cities So your playing on two fronts you have to indicate where both the clues and objects came from .An object might be in Rome but the clue to get is in Germania so you have to list name of both sites to move on"

(I got the gram already about two weeks ago, and I directed Marcus towards Huicton... but as I haven't seen anything posted about it I thought it best to post openly, in case someone would like to work on the idea with either Marcus or Huicton)

Marcus Aurelius Valerius
Huicton Moteuczoma

This is just one idea, and as it is a "contest" and a "scavenger hunt", people might be tired of them already, but...