Called to action by an unprecedented threat, these heroic souls formed a band to identify and remove the danger, for this was a noble goal (and backed by a noble's reward as well). Along the way, the tiefling mage Akemos begged to join in their quest, seeking answers of his own from the strange darkness that befell the land.
The scope of the disaster became apparent as the party encountered a band of marauding goblins, who threw themselves heedlessly against a superior force in their desperation to escape from the darkness.
The source of the trouble was the Tower of the Eclipse; made from solid shadow and out of phase with the rest of reality, this dreadful edifice could not be seen, only felt. Making a door to enter the other phase seemed to provoke the shadows, which called forth the spirits of the slain to strike down the party. At the summit of the tower was an entity known as the "Deathblossom"; destroying this being caused the phase space to vanish, leaving behind only a single gemstone, cold and black.