This is a double novel, based on concepts from TSR's espionage role playing game, Top Secret.
The first novel, Web Of Danger, is a fairly good novel about a civilian drawn into the spy game when he attends a gathering that gets dosed with a hypnotic drug. He meets a crack team of agents that face the criminal syndicate known as The Web.
The second is a pulp style thriller about Agent 13, and his struggle against The Brotherhood. He travels the world to prevent the head of the organization from rejuvenating himself, and encounters voodoo and vampires.