1803. The Napoleonic War. A Royal Navy warship is ordered to pursue an enemy frigate to the icy waters far south in the Indian Ocean. There it must capture the enemy ship and retrieve a mysterious sea-chest, contents unknown, failure not permitted. For the determined young captain and his eager crew, this already dangerous mission turns into a battle with a mysterious vessel that appears not in the sea, but, unbelievably, impossibly, in the sky above. But...