Michael O’Hara's parents are murdered and his inheritance is stolen. After two attempts to assassinate him he flees and joins a band of mercenary soldiers. He fights in wars in Africa, the Middle East, and South America. With the help of friends in the military community, he learns the identities of his parent’s killers, and returns home to confront them.

Michael, the main character in MERC, is the son of Sean and Margarita O'Hara from the book, THAT DAMNED IRISHMAN. His friend, Jesus, is the son of Miguel, one of the heroes of The SACRED LANDS and an important character in The AMBASSADOR, who saves the life of Margarita's grandfather, Rafael Alvarez, and serves as his lifelong bodyguard.