Is the book Crusade by Nancy Holder part of a series?

Yes, Crusade by Nancy Holder is part of a series called The Chronicles of the Vampire Hunter.

It's the second book in the series, following The Hunter. The series features a vampire hunter named Jason, who is also the son of a vampire.

Here's a list of the books in the series:

1. The Hunter (1999)

2. Crusade (2000)

3. The Assassin (2002)

4. The Reckoning (2003)

5. The Bloodlines (2004)

6. The Prophecy (2007)

Let me know if you'd like more information about the series or any of the books!