Marked (Eternal Guardians #1)

THERON – Dark haired, duty bound and deceptively deadly. He's the leader of the Argonauts, an elite group of guardians that defends the immortal realm from threats of the Underworld.
From the moment he walked into the club, Casey knew this guy was different. Men like that just didn't exist in real life—silky shoulder-length hair, chest impossibly broad, and a predatory manner that just screamed dark and dangerous. He was looking for something. Her.
She was the one. She had the mark. Casey had to die so his kind could live, and it was Theron's duty to bring her in. But even as a 200-year-old descendent of Hercules, he wasn't strong enough to resist the pull in her fathomless eyes, to tear himself away from the heat of her body.
As war with the Underworld nears, someone will have to make the ultimate sacrifice.