Carlino is a director and screenwriter, and in both capacities he's been involved in some famous films. I don't know if The Mechanic is a novelization of the movie or if it was before the movie, but I suspect the former. Not that it matters. The action is much like the movie, but the effect is a lot different because the book is much more an examination of Arthur Bishop's character. Bishop is a guy who looks into the abyss and sees the abyss staring back. All the time. Except, that is, when he's setting up and carrying out a hit. He's meticulous and careful, and when he lets down his guard even the tiniest bit, you know bad things are going to happen.
A guy like that shouldn't take on an apprentice, but Bishop does. He allows the son of an old friend (and victim) to become a part of his life. After that things get complicated, and the less said about them, the better for you to find out for yourself in either the book or the movie.
The book is short (144 pages), and a lot of it is more concerned with Bishop's mental state than with the action (though there's a good bit of that). There's a lot of very '70s stuff here, which you may find amusing. I found it nostalgic. I was bothered a little by the shifting points of view in some chapters distracting, but that might not bother you. It was fun to take a trip back to the '70s and to remember the Bronson movie. Maybe I'll see the new one (Carlino worked on the screenplay) one of these days.