Amid the shimmering, forested, hazy inland archipelago of the multitudinous Wavering Isles - tall islands rising from lakes and channels of immense depth - lake nations thrive, worshipping a strange entity they call the spirit dragon. This creature or demigod rises from the deeps once every seven years and leaves behind a gift if it is pleased with the sacrifices it receives.

The gift is a castoff shedding of enormous scales in long strips and sheets. Warlocks of the spirit wyrm can fashion these scales into the lower halves of hulls for their ships, which are otherwise made of hard and heavy dark mahogany. This grants the vessel some remarkable properties.

First is that the crew can cast lines overboard weighted with fragments of scale, and pulling on these ropes, can overturn the ship entirely even if the weights only bite into water. Once the centre of gravity tips beneath the water, the ship capsizes, but those on board are not harmed, for a shimmering bubble of air clings to all surfaces. Further, they can walk about and climb sails as though the ship were right way up.

While inverted, the ship likewise sails and functions as though it were above water; if there are high winds above, the sails fill and move the vessel more quickly. As such, it offers little protection from storms. Oars will also pull the ship along, although they don't need to poke into the air above to do so.

To an onlooker, the capsized ships can appear to be a variety of different things - a strange wave, a fog bank, a floating log, some rocks, or even an outsized crocodile, depending on the desires of the ships captain. Ghostwyrm ships, as they are known, can't engage in battle underwater as the shroud of air doesn't extend far beyond the hull and things connected to it, but they can surprise enemies and have been used to destroy far more powerful invaders.

Care must be taken not to grind along the bottom of the lake, river or sea where the ship is sailing, although all but the most dense weeds part and fall when the wreathing of air encompasses them.

Explorers of shallow wrecks and medium depth ruins under the waves have taken advantage of the marvellous properties granted to ghostwyrm ships to climb along ropes to a distance of about fifteen meters from the mast and clamber into long-lost areas in search of secrets and ancient treasures.