Part 1 of Jill Williamson's Epic Fantasy Series The Kinsman Chronicles
The god of the soil is furious. Volcanic eruptions, sinkholes, earthquakes--everything points to his unhappiness. At least this is what the people of Armania in the Five Realms believe.
Amid the unsettling state of the world around them, the princes of Armania live their lives focused more on who will claim the throne after their sickly father, King Echad, dies. That is until Prince Wilek's concubine turns up dead--beside her, a bloodied message that seems to have come from the mother realms.
Darkness Reigns is collected together with parts 2 and 3 in King's Folly.