The Hobgoblin's Fortress

From publisher blurb:

Pity Captain Dur-zagt. This grizzled hobgoblin mercenary captain faces a danger greater than any foreign foe as unruly goblins under his command plot to mutiny against him. That's where your party enters the story. His problem becomes your party's problem when they come upon a fort garrisoned by his company. The captain detains them, pending orders from farther up the chain of command. Will your party join the mutiny or sell out the mutineers to regain their freedom?

The Hobgoblin's Fortress is published under the Open Game License. It does not specify a particular campaign setting, and it allows you to integrate it into your own campaign world by filling in various details.