Eternity — Shayla Kersten

The Rememdiu (Eternity, book two)
Roger Malloy has devoted his life to the Secret Service until one assignment gone wrong destroys his career. Little does he know how the chain of events started by his contact with Lorcan MacKenna will end. Now on the wildest ride of his life, Roger finds himself drawn to a strange trio of people claiming to be immortal vampire hunters.

Adria has spent the last four hundred years looking for the Rememdiu, the one person capable of destroying the night demons, only to find a very uncooperative Roger Malloy. Although she knows he has the genetic makeup to be the Cure to the scourge of vampires, convincing him is harder than she expected. Her two men are more than willing to help her persuade him in any way necessary. Unknown to her is Roger's true nature and the real meaning of the Cure.

Longing for Eternity ( Eternity, Book Three).
Serena's love for Zaki surpassed death, but her transformation into a vampire has kept her separate from him for thirty-four years. Her heart and body crave him, but the natural enmity between vampires keeps their visits brief. Now fate twists its fickle fingers into her life and teases her with a solution. And a piece of her heart she'd thought lost forever.

Zaki has spent two millennia living by the rules of vampiric nature-alone. Sex was a means to blood, not love, until Serena entered his life and enslaved what was left of his soul. Now his longing for eternity with the one woman who captured his heart may become a reality. If they both survive long enough for the cure...

Fighting For Eternity (Eternity, Book Four)
Searching for a murderous rogue vampire, Watcher Estefan Garza's life is turned upside down by tragic loss and a surprise from his past. His bone-chilling loss is warmed by fires of passion reignited by vampire Karl Brandt.

On a quest to destroy a former friend, Karl is startled by Estefan and his mysterious companions. Karl can't understand why Estefan hasn't aged in seventy years. Unwilling to let him leave until Karl discovers the truth, he offers Estefan and his friends refuge and assistance for their common mission. As a bloody battle for Memphis ensues, Karl and Estefan bond between danger and destruction until all that remains separating them is a fight for eternity.

(The Cost of Eternity, Eternity, book one is available as a separate book.)