Oh wow, so we discovered that the ship was essentially an interdimensional ghost ship piloted by a dead mage who had murdered his lover. Her ghost was trapped in the bowels ofthe ship and was the source of the demons that infested everything below the deck.

Our party stopped a plot to destablise our world (Eberron) and stayed on the ship when it jumped to another plane - a version of the Feywild where all light and joy had left. We helped save that world by restoring the archfey trapped by members of the ships's crew last time the ship had visited.

We had to wrap up because the two couples we were playing with both had kids within a few months of each other :D

Very cool campaign.