Heart of the dragon
Searching for her missing brother, Grace Carlyle never dreamed she would discover a secret world populated by mythological monsters--or find herself facing a sword-wielding being whose looks put mortal men to shame.But there he was, Darius en Kragin, one of a race of shape-shifting warriors bound to guard the gates of Atlantis, and kill all travelers who strayed within its borders.Now Grace's life was in his hands, and Darius had to choose between his centuries-old vow and the woman who had slipped beneath his defenses and stolen the heart of Atlantis's fiercest dragon.
Science Fiction & Fantasy, Paranormal, Fiction, Romance, Atlantis (Legendary place)
Gena Showalter
Gena Showalter is a bestselling author of over thirty books in paranormal and contemporary romances, as well as young adult novels. Her novels have appeared in Cosmopolitan Magazine, and Seventeen Magazine, and have been translated all over the world. Source: Goodreads.com 
"Gena Showalter (born 1975 in Oklahoma) is an American author in the genres of contemporary romance, paranormal romance, and young adult. Showalter sold her first book at the age of 27, and has published over 25 books." - Wikipedia