Seattle-based indie developer Spiderweb Software has announced that Avadon: The Black Fortress, its 40-hour fantasy RPG that debuted for Mac systems last month, will release for Windows PCs on Monday.

Like the developer's Avernum and Geneforge series, which have a small but devoted following, this first chapter of a planned "epic fantasy saga" is a turned-based 2D isometric game. It features four unique classes, "many different endings", dozens of side quests, and hundreds of magical items.

Spiderweb sets up the plot:

"As a Hand of Avadon, ruthless and efficient enforcers of peace, your missions will take you to the 5 lands of The Pact and beyond. Battle those who seek to disrupt peace in the land while dealing with spies and assassins who wish to use the power of Avadon for their own gain.

As your comrades are picked off one by one it will be up to one stalwart Hand to steady the scales of justice. ... Learn the unique history of the five lands of The Pact and make important decisions on your journey that will reveal one of many endings."

You can find more information on Avadon: The Black Fortress, download a demo, and buy it for your Windows PC starting May 2nd at the studio's site. Keep an eye ouf for an iPad version of the game later this spring, too!