Something valuable has been lost, and the cast must find it. It probably doesn't really matter what the thing is, so long as its lost, and important to find. And perhaps well guarded.
Pros:
Straightforward structure that can be plugged into any setting.
Cons:
This is like 90% of published adventure supplements.
Fate Value: 2-6 depending on who or what is guarding it.
Example:
"You will find the lost Orb of Unobtanium.".