The Satanists — Philip R Benge

Rob Hinds is a secret agent who is quite used to combating alien spies, unfortunately, he is increasingly being asked to combat demons, and the Satanists who conjure them up. His opponent this time is the daughter of his last such enemy. Moira Bourbon wants her father back, unfortunately, the only way is to steal the knowledge from Tartarus, a demon dimension. To this end she kills, kidnaps and sacrifices to ensure she is successful. She even blackmails Rob Hinds into obtaining an ancient satanic device that will be necessary, if she is to enter Tartarus, her lever are the lives of his wife and her young sister.