Rusty Rutherford, recently fired IT manager of the city of Pleasantville, Tennessee, is currently the least popular person around: the city is in the midst of a ransomware attack. Unable to mitigate the damage, Rutherford is literally scorned by everyone. Rusty is en route to the local coffee shop for his daily visit, mere blocks from his apartment, dreading the expressions of rage and disgust on the faces of the other customers. Jack Reacher, retired from Army Intelligence, has just arrived in Pleasantville, hungry for a good meal, also heading for the coffee shop.

The two men's trajectories collide. Reacher interrupts an attempted kidnapping, quickly arrested for his trouble by local police. After a discussion with the lead (only) detective at the Pleasantville Police Department, Reacher learns about the city's current dilemma, ultimately refusing advice to leave town with Rusty at the mercy of police, the FBI, various gangs of thugs. Most critically, a foreign government has sent a force to steal security information buried in the computer servers Rusty delegated for disposal the day he was fired.

It's a dense plot with a changing cast of threatening characters, a stranger rolling into town who chooses to defend a man he's never met. That stranger, Jack Reacher, has skills, something Rutherford has as well, but only in relation to technology. Rusty's attackers are strangers, albeit with unmistakable intentions. It is not a situation Reacher finds acceptable, so he decides to sort the good guys from the bad and leave only when Rutherford is safe. From a detective in the police department to government agents, all are suspects until proven innocent, a list that grows with each new encounter. Pleasantville is a small place but a huge threat to the country as their mission becomes clear. Jack Reacher is Rusty's only defense against an army of foes.

After the original attack, the actions increase and bodies pile up. Rusty is determined to put his IT program back together and defeat the ransomware attack, unexpectedly joined by his former IT partner, ex-FBI agent Sarah Sands, and guarded by Reacher. The three recover the servers; Rusty and Sarah reassemble the system in a safe place while Reacher moves on the attackers attempting to kidnap Rusty, finding potential allies along the way. He assesses the most serious threats, from an eccentric millionaire who lives in the city's notorious "Spy House" to a random group of white supremacists. From this perspective, he focuses on a small force sent from a foreign country, most likely Russia. These are the most menacing and dangerous force, a special agent, their most efficient strongman arriving soon to deal specifically with Reacher.

The hand-to-hand combat is relentless, the back story born in the remnants of World War II, the denouement begun in an underground bunker, a warren of tunnels ending in one last chamber fitted with tools for torture. The past morphs into modern warfare once Jack leaves the bunker and learns the real threat at the heart of Rutherford's attempted kidnapping. The Sentinel is a thriller with all the bells and whistles, from stealthy forces to the cyber threat that has become a part of modern warfare. The threat is serious, a fight Jack Reacher can't fail to dominate, no matter how many bulked-up bad guys come at him.

It's the same old fight, good guys versus bad, the enemy making mischief in a small-town America when a stranger walks into town and joins fight. Reacher may not be well-versed in technology, but his instincts are second nature, a solitary soldier for justice. Rusty defeats the ransomware attack, Pleasantville restored. Time to move on.

Lee Child adds his brother, Andrew, as co-author of The Sentinel, perhaps to pass his protagonist on for a fresh perspective. The formula that has garnered a legion of fans may be a little worn but is still filled with action and the triumph of good over evil.