I'm about to start a campaign that takes place on a pirate ship. Low magic fantasy setting, loosely based on the Caribbean in the 1600s. Much of the action is going to be centered around various elements of the pirate's code. As such, I'd really like to include a scenario in which the party has to identify the crew member who's been stealing and hoarding loot (or a government agent who has snuck on board. Not sure which yet). Once they catch the culprit, they'll have to decide whether to deal with him themselves or turn him over to the Captain's … draconian policies.
I can think of a number of challenges that might be appropriate – talking to various crew members, setting up watches, searching bunks while suspects are elsewhere, but I'm worried that I won't be able to pull the scenario off while keeping all party members involved.
In the past, when I've tried to run investigation or diplomacy based scenarios, I find that the party-face character tends to dominate the action, leaving the less thinky characters to twiddle their thumbs. Conversation, unlike combat, isn't turn-based, so it's hard to make sure everyone gets a chance to be in the spotlight. Plus, investigation often necessitates splitting up, which is a pain in the butt to run while keeping everyone interested.
So basically, my question is twofold:
How can I design investigative challenges that use a wide variety of abilities and reward teamwork?
Is there a good way to handle parties splitting up to gather info without bogging down the game?
I'm using Fate Core, but would prefer system-agnostic answers.