Decades ago, when he was a young CIA analyst, President Jack Ryan, Sr. was sent on what was supposed to be a simple support mission to investigate the death of an operative who had been looking into suspicious banking activities at a Swiss bank. Ryan's dogged tenacity uncovered not only financial deceit, but also the existence of a KGB assassin, code-named Zenith. He was never able to find the killer. But in the shadowy world of covert operations,...