The first lesson readers of mystery fiction must learn is that nothing is actually as it appears to be. The first lesson for writers of mystery fiction is that the untrue must appear to be true.

Few writers of contemporary detective stories are able to achieve this daunting goal with the devious dexterity of James W. Hall, whose new novel, “Magic City” (St. Martin’s, 308 pages, $24.95), underscores his position as one of the masters of this art. He is at the very top of his form in this, the ninth novel about Thorn, the reluctant hero who prefers to live peacefully in the Florida Keys but somehow seems to find trouble—or, more accurately, it finds him.

From an opening scene that charges out of the box like a greyhound on amphetamines, to the climactic denouement that will leave the reader as limp as two-month old kale, the pace of “Magic City” never slows. As usual with Mr. Hall’s books, there is much more than one exciting scene after another.

It is Miami in February 1964: “A dozen armed men in stocking masks came for the Morales family.” Mother, Father, and daughter are killed, along with five men whose job it was to protect them. Escaping the slaughter are the two sons, Carlos and Snake, who quickly become celebrities when they are taken in and adopted by the young mayor, Stanton King, and his beautiful wife, Lola.

Jump ahead 40 years. Carlos and Snake now work for their adoptive father. When Stanton attends an exhibition of photographs, he sees one from the first Cassius Clay–Sonny Liston championship fight that could prove embarrassing for him. He sends his sons to steal the print from the photographer and the other print, which happens to hang in Lawton Collins’s house. A former Miami cop, old and mostly senile, Lawton is the father of Alexandra Collins, Thorn’s girlfriend.

Had Thorn let the brothers steal the picture, the terror and bloodshed that follow never would have occurred, but that just not the way it is for the tanned outdoorsman who loves the Florida Keys.

“In the secret marrow of his bones,” Mr. Hall writes, “Thorn considered himself a peaceful man. Meditative, a student of sunsets and sunrises, and the trajectory of gulls and egrets and the lazy lofting flight of great blue herons. A man who hungered for nothing more than the love of a woman, the tug of a large fish on his life. Simple [stuff]. But the years had proved a steady contradiction.”

That is certainly true for Thorn. Beginning with the stunning “Under Cover of Daylight” in 1986, he has made a reluctant appearance in nine novels, all of which are first-rate but none more frustrating or complex than “Magic City.”

The frustration is that the woman he loves blames him for everything that has gone wrong.

The complexity arises from the fact that the annihilation of the Morales family and its motivations, rooted in distant history, are incomprehensible to Thorn.

Attempting to fathom such a despicable act, Thorn confronts Snake, confident that he has it figured out. When Snake, who witnessed the murders as a 12-year-old, tells him what it was about, Thorn refuses to accept his explanation.

“It was always about love,” he believes. “Always, always about love. Lost love, love denied, the obsessive hunger for love. Parental or romantic. Whether it was twisted or pure, fulfilled or unrequited, love was always at the source.”

Well, maybe not. Certainly, there was love, not all of it fulfilled, not all of it requited. There was romantic love, and parental love. Some of it twisted, some of it pure. But there was much more at stake. There was Cuba.

A year after the failed plan to rescue Cuba from the communists at the Bay of Pigs, most of the enormous Cuban population in Miami still dreamed of the day when they could return home. Jorge Morales, a simple cane-cutter in Cuba before the revolution came down from the hills, was the leader of one of the groups that never gave up that dream.

The CIA connection that Mr. Hall eventually posits in this terrifying work of otherwise credible fiction is too far-fetched to accept, too uncomfortable to believe, even for an instant. The only problem is that it is based on recently declassified documents.

Mr. Penzler is the proprietor of the Mysterious Bookshop in Manhattan and the series editor of the annual “Best American Mystery Stories.”