One More Sunday — John D. MacDonald

Welcome to the Eternal Church of the Believer, where devout workers operate state-of-the-art computer equipment to process the thousands of dollars that pour in daily and where hundreds of prayers are offered by armies of believers.

Roy Owens arrives there after his journalist wife disappears while doing an exposé on the Eternal Church of the Believer. Embroiled in a desperate search for her, it is not long before he uncovers a multimillion-dollar organization that hides the vices and human failings of the people behind the church.