Books like The ravagers by Donald Hamilton

Jack Reacher, an elite U.S. military investigator, faces a deadly conspiracy after a two‑star general’s murder in North Carolina, leading him from rural army posts to the streets of Paris in a high‑stakes hunt for truth.

A mother's nightmare returns as she discovers her children are missing in Cape Cod, Massachusetts, and must confront the shadowy figure who murdered her first children.

Bob Lee Swagger, a Vietnam veteran, returns to Idaho for a quiet ranch life but finds that the memories and unresolved threats from his war days still haunt him.

A thriller set in the aftermath of 9/11, exploring the dark side of the United States' war on terrorism.

"I very much need to be dead." These are the chilling last words left by a man who had everything to live for but took his own life. In the void that remains stands his widow, FBI agent Jane Hawk, surrounded by questions destined to go unanswered unless she does what all the grief and fury inside her demand: Find the truth, no matter what. People of talent and accomplishment, people seemingly happy and sound of mind, have recently been committing suicide in surprising numbers. A disturbing pattern is beginning to emerge. Jane is determined to give up everything to find out why. And if that means going rogue and becoming America's Most Wanted, then so be it. Those arrayed against her are legion, and devoted to protecting something profoundly important-or terrifying-enough to exterminate any and all in their way. But Jane is as clever as these enemies are cold-blooded, as relentless as they are ruthless. And she is driven by a righteous rage they can never comprehend. Because it is born of love.

When a female agent is killed in Mexico before Helm can complete his mission, he is forced to partner with her sister to protect multiple scientists and Congressmen and unravel an espionage plot.