The Power That Binds — Mark E. Cooper

Book two of The Devan Chronicles. A year on from Julia Morton's arrival at Fortress Athione, an uneasy truce is being maintained between Deva and her enemies, but the Protectorate never rests. Believing himself destined to rule, Lord Mortain unleashes General Navarien upon the north in an effort to bypass Julia's guardianship of Deva's western borders.

Meanwhile, having rallied the scattered forces of a dead traitor behind him, Rowton of Ascol moves ahead with his plans by murdering the King. With the King dead, and the lords vying for his throne, Julia tries to ensure the right man is chosen for the job. When things go wrong, she resorts to force, but sorcerers won't be pushed, and soon the lightning bolts fly again over Deva.