The Sentinel is the twenty-fifth book in the Jack Reacher series. I haven’t noticed any issues with the transition from Lee Child writing alone to coauthoring with Andrew Child. It is still classic Jack Reacher. However, Reacher is becoming a dinosaur in his investigative methods. He has never carried a cell phone, doesn’t drive a car, doesn’t know how to operate a computer. He looks up phone numbers and addresses in the paper director, if there even is one. It looks like Rusty Rutherford, the IT consultant that Reacher is protecting from all of the bad guys in this story is going to give him a little help in bringing himself up-to-date on the technology side of things, so you can look forward to Jack Reacher with a smart phone as the series progresses. This could open up a whole new world for Reacher. Online searches and maps, calling an Uber, Amazon delivering to his door… the possibilities are endless.