Mackenzie Flynt has retired from the United States Navy after twenty-two years of distinguished service, most of them with the Naval Criminal Investigative Service. Divorced by his wife, his military career over, Flynt migrates north from San Diego to Vancouver, Washington, where he is to become Director of Security for a high tech firm. When the job does not pan out, he finds himself in a strange town with no friends, limited funds and no job, so decides to get a state license and hang out his shingle as a private eye.
While being treated in a hospital emergency room for injuries suffered in an auto accident, he is befriended by Dr. Melissa Bauer, the beautiful and talented attending physician there. Discovering his vocation, she hires him to look into a harassment complaint made by her elderly mother, a resident of nearby Skamania County. Finding evidence of vandalism, arson and threatening notes, Flynt sets out to discover the identity of the mysterious bidder attempting to acquire the old woman's property. But therein lies the mystery. The man apparently lives in an authentic mountainside castle accessible only by a private and guarded gate and road. Even more curiously, no one in the surrounding countryside can ever remember meeting or seeing the man.
As Flynt launches a probe into the hermit's affairs, bad things begin to happen. He discovers that both a lawyer hired by his current client and a cub reporter who wrote a story about the castle dweller have gone mysteriously and permanently missing. While asking locals about the man, Flynt catches a glimpse of an old nemesis who tried to kill him eight years earlier. When one clue meshes with another, he concludes that this face from his past and the mystery man in the castle are somehow linked.
Against all wisdom, he finds himself falling hopelessly in love with his client, the young doctor. When the doctor's mother dies suddenly, Flynt concludes that foul play is involved and launches an all-out probe. Since his would be killer is still wanted by NCIS and major governments around the world for gunrunning and murder, Flynt enlists the help of his old pals at NCIS and soon finds himself on contract with the Navy to hunt and bring to justice the nefarious felon. In the process he means to also discover who killed the good doctor's mother, and why.
Assisted by a wily old newspaper publisher, Flynt learns of a connection between the man in the castle and a riverside shipping and receiving facility. Risking a night dive in the treacherous waters of the Columbia, Flynt embarks on a dangerous reconnaissance mission in which he discovers a ship loaded with stolen U.S military hardware, just before being detected and fleeing for dear life. He now has his linkage between the two villains, one as a buyer and the other a seller of illicit weapons.
Due to a temporary personnel shortage, his NCIS handler insists upon involving the Bureau of Alcohol, Tobacco, Firearms and Explosives. Despite early conflicts between Flynt and ATF Agent Celia Hart, a working arrangement is reached to place the shipping facility under around the clock surveillance until sufficient probable cause can be legally gathered for a raid.
With help from NCIS forensics, Flynt proves that the doctor's elderly mother was slowly poisoned until she suffered convulsions and a coronary. A youthful NCIS probationer assigned to help Flynt proves invaluable in unraveling the multiple identities of the castle's keeper. Flynt, through an intermediary, elicits an invitation to the castle, ostensibly to strike a deal in which the deceased woman's property can be acquired by the man living there. As an overnight guest, Flynt executes a narrowing moonlight survey of the facility before being caught and cornered by his one-time assailant, also a guest there. The confrontation resolves in mortal combat, leaving Flynt the imperative of hiding the man's body and getting back into his room before daybreak without being seen.
The devil's bargain is struck: the land and immunity for the guns on the ship, cash and the surrender of the now dead guest to NCIS. When Flynt returns to report the proceedings he learns an awful truth. The castle keeper has kidnapped his lover and holds her hostage there pending completion of the deal.
In a deadly game of do or die, Flynt leads agents of NCIS, ATF and the County Sheriff's department in a night assault through a driving snowstorm against the nearly impregnable and heavily defended castle above. Hanging in the balance are their lives, and that of the hostage there hoping against hope for their arrival. But success comes at a price, and there are yet more surprises. The Creed Conundrum is not a read for the faint of heart. Plan to stay up late.