Promised by Blood — Samantha Snow

When lovestruck teenagers Holly and Tristan promised that they would marry each other when they were adults they both meant it. But then Tristan mysteriously disappeared from her life and it seemed as if that promise was going to be broken forever. However, a decade later and Tristan is back and ready to make good on his promise but only after he reveals his dark secret to her. That secret is that he is a vampire. And for them to be together she must become one too....