Falconsaga by Robert Winter

In modern-day Iceland, a place of glaciers, volcanoes, and legends, the Norns have foretold a sorcerous invasion that could destroy everything.
Magnús, one of the huldufólk, is driven by the murder of his human lover a century ago to save those humans he can, and to figure out what is behind recent troll attacks on tourists. But the Norns have spoken. He must protect Altair, a young human from Boston, who is bringing a dangerous magical force to Iceland. If Magnús fails to keep Altair safe, the country will fall to a sorcerer called the Black Priest. Yet if Altair lives, Magnús will meet his doom.
For his part, Altair is a graduate student bullied to visit Iceland by mentors who seem to have their own agenda. He knows nothing of elves, sorcerers or prophecies. Suddenly, the handsome, mysterious Magnús is guiding Altair around Reykjavik and into danger. A witch, a berserker, and more elves are along for the quest across Iceland's forbidding landscape. And why does everyone keeps calling Altair "the Falcon"?
An elf and a human with a shared destiny. Will they solve the mystery linking their fates before it is too late for all Iceland?