This is the closing a trilogy of 3 books; Mr. Mercedes, Finders Keepers, and End of Watch. It has the same villain and many of the same characters.
Retired detective Bill Hodges, and investigative partner Holly Gibney, have worked on this case from the very start (all three books).
"Mr. Mercedes has previously claimed sixteen lives when he drove a stolen Mercedes through a line of job-seekers at a local job fair
Brady Hartsfield, the mass murderer, has now acquired psychic powers. He wants to go after Hodges, and begins an online cat-and-mouse game between the two, that evolves to one with real-life consequences.
Besides going after Hodges, he has found ways to convince the innocent people he failed to kill in the past to kill themselves. An increasingly desperate Hartsfield, becomes bent on leaving his mark on the world.
Brady doesn’t like being trapped in a unmovable body but with some technology and other creepy stuff he is more dangerous than ever. The technology used is anything but modern day and his computor like tool is really like using Pac-man, but it works and is effective.
It is indeed the “End of Watch” for the villain and for the the hero. Each book easily could stand on its own, but they work a long plot that finally comes to be a typical Stephen King larger story.