Tom Clancy Zero Hour

Kim Jong Un's counterpart in this story, the ruler of North Korea, is gravely injured, and the damage sets off something no one planned for. His incapacity trips a dead-man's switch that wakes a network of sleeper agents buried across South Korea, while back in the North, rival figures begin to fight over who will take his place. Jack Ryan, Jr. lands in Seoul on what should be a routine trip, meeting a possible new recruit for the Campus. Instead he finds the city under attack as North Korean operatives unleash a wave of violence. With the peninsula sliding toward a second Korean War, an unknown woman's voice from inside North Korea offers him a way to halt the descent. Whatever she wants in return, though, may cost more than Jack can pay. This is a Jack Ryan Jr. thriller in the Tom Clancy series, written by Don Bentley.