Think of Lee Child’s “The Affair” as the long-awaited origin of Jack Reacher.

Though the book came out a dozen years ago, it took 16 years for Child to finally tell the story of the events that led to Reacher leaving his job as an Army military police major and set him wandering the United States as a man without a home or any property except for the clothes he’s wearing, some money and his travel toothbrush.

In this book, a flashback to when Reacher was still a military police major, he is assigned to go undercover to investigate the death of a young woman in a town that’s home to an Army base. While he quietly enters the Mississippi town, another military major has been officially assigned to investigate the base; this major has shut down the base leaving the small town nearly as deserted as a ghost town.

Reacher meets the town’s beautiful female sheriff, a former Marine MP who quickly breaks his cover. Soon, Reacher and the sheriff are working together and getting to know one another more than just professionally.

The signposts are here for regular Reacher readers.

Reacher takes a bus to get to the Mississippi town, which is part of his regular mode of travel in his post-military life. Instead of washing his civilian clothes, he simply buys new ones then throws the old clothes away – his usual wardrobe practice. He carries a folding travel toothbrush, same as he has done in the previous post-military novels. He acquires a taste for diner food and strong coffee.

It also sets the stage for the events in the first Reacher novel, “Killing Floor,” with references to Reacher’s older brother traveling to Georgia.

“The Affair” is as much of an origin story as Spider-Man being bitten by a radioactive spider or Harry Potter’s parents battle to save their infant son from Voldemort.

And it only took 16 novels.

More sensitive readers should be warned, too, that “The Affair” contains far more steamier passages than most of the previous Reacher novels. Far more details between Reacher and the Mississippi sheriff.

It is also one of the books where Child writes with Reacher as the narrator. Which never feels completely natural, given Reacher’s silence in most books. He’s plenty intelligent but it’s difficult as a reader imagining him using so many words to tell a story and even harder to imagine who would inspire him to tell his story. As he notes on page 60 of “The Affair”: “I said nothing. I’m good at saying nothing. I don’t like talking. I could go the rest of my life without saying another word, if I had to.” Then, he narrates another several hundred pages.

“The Affair” also includes the bonus material of a Reacher short story, “Not a Drill,” with Reacher in his usual bumming around America mode of being. A nice extra touch.