More technothriller than spy thriller, but look up Christopher Farnsworth's Nathaniel Cade series.
It's based on the premise that an urban legend (or perhaps true, but certainly Fortian) about President Johnson (the first one) pardoning a man accused of being a vampire.
Nathaniel Cade is a devout Christian who knows he has become a soulless monster forever removed from God's grace, but he's also a patriot who has been geassed by Marie Laveau to follow the President's lawful orders.
There are references to him leading Elliot Ness at the Innsmouth raid, Johann Konrad succeeded, Serbian werewolves, evil cults plotting to destroy America from within and without (because the US is the manifestation of a magical ritual preformed by the founding fathers to keep the Great Old Ones out of our world), serial killers, at least three evil conspiracies, relics, fencing, terrorism, references to zombie outbreaks near Pittsburg, frankensteinian monsters in Texas and New Jersey... I know I'm forgetting tons.
Four books out so far, the first is titled Blood Oath.
