First Light by Elizabeth Hunter

In the Shadowlands, strangers wear familiar faces, myths are reality, and lies hide behind the most beautiful stories.

Lachlan Murray disappeared without a trace. As his girlfriend, twenty-nine-year-old Carys Morgan refuses to accept the police’s explanation—that he simply left her. She travels to Scotland to seek help from Lachlan’s twin brother Duncan, and learns she was right—Lachlan didn’t leave her, he left her world to return to his own.
The Shadowlands are a mirror of the world Carys knows. Every human in her world also exists in this one with one key difference—magic.
Humans aren’t supposed to be able to wield the magic of the Shadowlands, but when Carys learns she can talk to dragons, she’s drawn deeper into a complicated world that would as soon kill her as keep her. And if magic and murder weren’t enough to overcome, she must navigate complicated feelings for two identical men from vastly different worlds.