Generally, Jack Reacher is a lone wanderer.

He strolls into town, stumbles upon a situation, and uses his ludicrous stature to put the world to rights. Job done. But on TV, the formula is a little different. For the most part, Prime Video’s Reacher is hailed as a faithful take on Lee Child’s novel series, successfully capturing the spirit of the stoic man-mountain (helped by the spot-on casting of the gigantic Alan Ritchson).

But the biggest change the show makes is keeping a more consistent cast of characters orbiting its central hero – particularly Maria Sten’s Sgt Frances Neagley.

While Neagley only appears in a small handful of Child’s books (and notably isn’t featured in first novel Killing Floor, which provided the basis for Season 1) she’s been a significant presence in the show from the very beginning. And there’s a very specific reason why.

“Neagley was a strategic decision. The one thing you cannot do on screen that you can in a book is have the inside of somebody’s head,” Child tells Empire in the new issue. “Reacher thinks a lot, and there are pages and pages of Reacher puzzling things out.

You can’t write an eight-minute scene with Alan Ritchson sitting there, thinking. So we needed a secondary character to bolster the exposition.” Cue a larger part for Neagley, even in adaptations of stories she didn’t appear in on the page.

From there, the creators of Reacher have followed whatever path makes most sense. Since Child’s novels are generally designed to be read in any order, Season 2 adapted 11th book Bad Luck And Trouble. And next, Season 3 will adapt Persuader, the 7th Reacher novel.

“There was no reason to do them in order,” Child says. “We had massive discussions about it. The thinking went like this: Killing Floor introduces Reacher as a person.

So, which book shows his professional life, and what he did while he was in the Army? The result was Bad Luck And Trouble.” That’s the thing about Reacher: he plays by his own rules. Given how absolutely massive he is, who’d argue with him?

Read Empire’s full Lee Child interview – talking the film and TV adaptations of Jack Reacher over the years – in the Star Wars prequels 25th anniversary issue, on sale Thursday 15 February. Reacher is streaming now on Prime Video.