Tom Dugan is a marine engineer.
He is also, as the series progresses, a part-time, unofficial agent with the CIA but he would never think of himself that way. He knows in his head that he is first and foremost a marine engineer and he likes it that way. He loves ships and the sea and even the business end of things, though that gets boring after a time.
Even more than an engineer, a man who understands the ins and outs of operating seagoing vessels for profit, be they cargo ships or tankers, Dugan has been for many years prior to the first recorded adventure a troubleshooter. If a company has a ship in dry-dock that is not getting finished, Dugan is hired to investigate why. If there is a ship for sale in some distant port, Dugan is the man to check out whether the price is worth the goods. He is highly respected and much sought and when he voices an opinion in his field, smart people know to listen.
Dugan is a widower who still misses his wife but enough time has passed that when he is thrown into close contact with a lovely female MI-5 agent, Anna, in a joint venture with the CIA, they become intimate. Now as this talented amateur proceeds deeper into the fight with the enemy, he has an experienced companion.
There is no doubt that Dugan is a novice. He is not, however, lacking in common sense and intuition and since his area of expertise is ships and shipping, when the bad guys strike at the West using those items, he is the best man to lead the fight against them.
Also working with Dugan is his boss, Alex Kairouz. Kairouz is the founder and CEO of a large and prosperous shipping operation and Dugan, an old friend, is the first man he calls when problems arise. When Kairouz got into trouble at the hands of some very bad men in the first book, it is Dugan who came to his friend's aid though it almost landed him in prison as a result. When that adventure ended, the two were offered the unofficial role in the CIA/MI-5 joint affair.