The hero must go underground because of demons. They stole the gemstone from humans, because they were jealous of the good magic it brought to humankind. They broke it up and spread it throughout their dungeon, to hide it.
This game is not just a "shoot-em-up"; it has many features that require strategy and thinking. It includes a pause feature which helps players map and also freeze a room, to see what is running toward the player. The game also has a save feature, which is useful just before entering a new room: if the player's character is ambushed, they can give him another chance.
After killing opponents, the Gemstone Warrior has the opportunity to search their bodies for treasure. Monsters carry arrows, and also "magic bolts." The latter are interesting, as they destroy treasure too, as well as the player, should he be too close to the explosion. Magic items abound, and help the warrior make it through the caverns. Some magic items are traps too; there is a healing potion bottle that is similar to a poison bottle. Other magic items include effects to freeze opponents, turn the player invisible, hide him among monsters with an illusion, annihilate all opponents in the current cavern, and cure disease.