"No. He didn't. Don't worry. Before the ransomware attack he pressed the town to buy a backup systemfor all the computers. The wouldn't come up with the cash so he tried to build one of his own out of spare parts. It was supposed to overwrite whatever was on the server, but that didn't happen. That's how he knew it had failed. He was so mad about it he threw all the equipment in the trash."
Lee Child and Andrew Child, The Sentinel, Ransom House 2020
I've read all twenty-four of Lee Child's previous Jack Reacher novels and posted comments on six of them on this blog. The co-authorship of this volume is not successful, mainly because the plot is too confusing and the usually reticent Reacher blabs too much. The beginning is similar to the earlier books -- Reacher drops into a new town and immediately has to help someone who in this case is being kidnapped -- but then the plot, involving computer programs, becomes almost impossible to follow, as Reacher battles Nazis and Russians attempting to interfere in American elections. My guess is that possibly Child is tired of Reacher and wants to pass him on to younger brother Andrew (who writes novels under the name Andrew Grant; I have read none of his novels). I also think it is likely Andrew became involved to help with the computer details, as Jack Reacher previously did not use computers or even cell phones. Certainly co-authorship can work, as in the case of Per Wahloo and Maj Sjowall, whose brilliant Martin Beck novels I am currently rereading, and I have no problem with Jack Reacher evolving, but The Sentinel changes Jack too abruptly.