Prerequisites: Attain level 2 friendship with Russo and Dean
Reward: Two Moon Cloves
Unlocks: --
To unlock this quest you need to make at least one friend, and possibly two. Reach the second level of friendship with both Russo and Dean - it's possibly only Russo, but at this point I'm not sure - then head to Moonbury Park. (It triggered for me at 8:30, if that helps.) You'll watch a scene where Dean admits that he's lost a package, and the mighty Detective Russo declares that he's on the case. You, of course, get to be his assistant.
Head to the Arcade Centre in the basement of the Lazy Bowl Tavern between 10:00 and 17:00. The whole group will commence a search for Dean's package, but it's not there. Helene mentions Zeke stopping by earlier, and Russo demands you find Zeke while he and Dean search elsewhere. Zeke is found throughout Moonbury on any given day, so unless it's nearing nighttime and you want to search near his tent you should have your dog track the old guy down.
Track down Zeke and he'll admit to finding the package... only Kipps, his cat, wrecked it. All that's left is an Empty Pendant Box that Zeke hands over. Take it to Russo - again, you're best off using your dog to find him - and everyone will hold another meeting. It appears that the pendant inside the box was for Osman, and, uh... Russo might know something about it. Case complete?