Adept Series by Katherine Kurtz, Deborah Turner Harris

He is Adam Sinclair, nobleman, physician, scholar, and Adept. A man of learning and power, he practices ancient arts to fight evil. Now his beloved Scotland is defiled by an unholy cult of black magicians, and only he can stand against them.

Psychiatrist Adam Sinclair, also known as the Adept, leads his loyal Huntsmen against the Lodge of the Lynx--an unholy sect in possession of an ancient Druidic artifact endowed with unimaginable power.

Adam Sinclair, the Adept, must locate the stolen Seal of Solomon-an artifact under the care of the Knights Templar-before dangerous forces unleash the demons the seal has kept bound for centuries.

Adam Sinclair, the Adept, faces mankind's most dire threat--a cult older than Christianity, with the power to resurrect a new, demonic Third Reich.

Sir Adam Sinclair, the mystic historian known as the Adept, has emerged victorious from his encounters against the forces of darkness. But now he faces the most unthinkable crime imaginable against his kind: murder.