The BloodStone - Cauldbearer Stone, #1

When a spell inadvertently creates a tear between the realms of men and the dark ether, it releases a malevolent evil. Aodhán is sent to uncover the source, and his quest leads him to Danni, a beautiful Cauldbearer, a wielder of magic, who is being stalked by the demonic others-fallen Sidhé who will do anything to capture her and use her ability to direct magic using the Bloodstone. Ordered by the Council of Elders to eliminate any threat to the realms, Aodhán instead saves Danni as she is being pursued by a demon, only to ignite an attraction between them.
Aodhán tries to fight it, knowing that his fiancé, Branwein, waits for him in his own realm, but as the attraction grows he yields to it and takes her to Scotland, to protect her in the fortress known as the Keep. But Aodhán has underestimated the power of the Sidhé, and soon the two are fighting for their lives. Can he keep Danni alive long enough to reverse the tear? Or will they both succumb to the forces of darkness?