The Oath (en Inglés) - John Levin MD

Jon Sloan is the kind of doctor people trust with their lives-brilliant, calm under pressure, and capable of miracles when seconds matter. In a quiet Kansas hospital, he saves the broken, the bleeding, the dying... and sometimes, when no one is watching, he decides who doesn't deserve to live at all. The world calls him a hero after he stops a mass shooter with flawless precision-but what no one sees is what that moment unlocked inside him. Because for Jon Sloan, the line between saving a life and taking one isn't a line at all.

Recruited into a covert government unit that needs a man who can think with a scalpel and a gun, Sloan is pushed to the edge of human capability-doctor and soldier, healer and executioner. As missions escalate and his control sharpens, one question begins to haunt those around him: is he protecting the world... or perfecting something far more dangerous? In a story where morality is measured in seconds and blood, The Oath asks how far a man can go before the promise to do no harm becomes something else entirely.