Like Philip Roth’s “The Plot Against America” and Philip K. Dick’s “The Man in the High Castle” before it, Ben H. Winters’ “Underground Airlines” fits snugly in the genre of speculative “What if?” fiction — the kind aimed at shaking up our jaded understanding of freedom and democracy.

In both the Roth and Dick books, a weaselly America sells itself out to the Axis powers during the 1940s. While there is no lack of relevance in either book — particularly at a time when demagoguery is on the rise — it’s possible to read them from a safe distance.

Even with its entertaining crime fiction trappings, “Underground Airlines” allows no such detachment. In Winters’ thriller, set in an alternative present, slavery legally exists in four Southern states — “the Hard Four.” Though Georgia and Kentucky rid themselves of the hideous practice in 1944, full-scale abolition never took place; there was no Civil War. The story reverberates eerily and unsettlingly with the anti-black violence, profiling and open racism that have fueled the Black Lives Matter movement.

Victor, the nearly 40-year-old black protagonist of “Underground Airlines,” is both victim and victimizer. A onetime slave, he has been forced into working undercover for the U.S. Marshals, tracking runaway “Persons Bound to Labor.” He receives his orders via phone from a droning superior who follows his every move via a surveillance device implanted in Victor’s neck.

Long past feeling guilty about bounty hunting his fellow African-Americans after six years on the job, Victor has come to Indiana in pursuit of Jackdaw, a 27-year-old escapee from Garments of the Greater South, an Alabama textile plantation where more than 4,200 slaves toil. With his superior role-playing skills, Victor (who goes by many other names), gets next to Barton, a white parish priest who heads up a secret abolitionist group that transports runaway slaves north via the so-called Underground Airlines, which “flies on the ground, in package trucks and unmarked vans and stolen tractor-trailers.”

The plot thickens when Victor befriends Martha, a distressed young white woman with a black child and a hidden agenda of her own. In pursuit of an envelope containing information the slave states will do anything to keep secret — a classic suspense-novel MacGuffin — they sneak onto the Alabama plantation, where, haunted by a violent act, Victor confronts his double life.

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In his acclaimed “Last Policeman” trilogy, Masters showed off his mastery of edgy, sardonic wit — there’s nothing like an asteroid speeding toward Earth to bring out the black humor in people. “Underground Airlines,” too, boasts plenty of priceless details. We learn that soul godfather James Brown defected to Canada, having tired of leading his band of “talented slaves” up north to demonstrate how happy everyone was down south. Cataloging the “172 varietals of African American skin tone” — Victor’s is “moderate charcoal, brass highlights, #41”— is an important tool in tracking down runaways.

Still, imbuing the proceedings with a deep sense of morality, sparing neither North nor South, Winters allows himself to cut loose in preacherly fashion: The “idea drifts up and out . . . like chimney smoke, black gets to mean poor and poor to mean dangerous and all the words get murked together and become one dark idea, a cloud of smoke, the smokestack fumes drifting like filthy air across the rest of the nation.”

That Winters is white adds a layer of complexity to the book. Perhaps acknowledging his audacity in taking authorial ownership of the slavery narrative, he has a black Indiana cop who works with Barton criticize the priest for having a “ ‘Mockingbird’ mentality” — believing that “the white man is the saver, the black man gets saved.”

In the end, “Underground Airlines” tells us, we all need to be saved, and we all need to do the saving, from dehumanizing practices and attitudes that don’t need to be institutionalized to tear this supposed land of freedom asunder. As Barton tells Victor, “This is a hard situation we put you in. But you must see it . . . Here you can be a soldier — you can be good, my son. You can do good.”