The Temptation of John Haynes. Isis, #4

The Devil doesn't like John Haynes. To take his soul, Lucifer recruits E'steem a beautiful she-demon to seduce him. If she can persuade John to compromise his beliefs and values, he'll allow her to join his Elect, a cadre of powerful demons in his inner circle. To balance the playing field in E'steem's favor, Lucifer isolates John by having him fired from his job . Unemployed and emotionally vulnerable, John eagerly takes what he thinks is the job opportunity of a lifetime as CEO of Morris Phillips.
Distracted by his new high-powered job and its many duties, he has no idea that Lucifer secretly controls the multinational corporation or that his live-in assistant is a she-demon placed there to corrupt him. However as E'steem becomes romantically involved with John, she's torn between achieving her theocratic aspirations and saving the man she loves from eternal damnation.