The Defiant by Paul Dengeligi (Casca Series, Book 24) from Books In Motion.com

In the bustling medieval port of Venice, Casca saves a boy's life, and becomes embroiled in an ancient blood feud. It seems that the eager young man, Marco, is desperately in love with a girl he cannot have...a Donatello. The powerful Donatello family would sooner kill the lowborn Marco than allow him into the family. But, that is something Casca will not allow to happen, even when he finds himself caught in the middle of a bloody, merciless war.