It tells the story of Jordan Lyman, who is a widely unpopular President of the United States. His unpopularity stems from his decision to ratify a treaty with the Soviet Union that will supposedly result in both nations simultaniously destroying their nuclear weapons under international inspections. This move is extremely unpopular with segments of the Republican Party and the military, who believe the Soviets cannnot be trusted.
Eventually, President Lyman and his closest advisors learn from a high-ranking Pentagon insider named Colonel Jiggs Casey that the Joint Chiefs of Staff, led by the charismatic Chairman James Scott are secretly plotting to stage a coup d'etat and overthrow the President.
The rest of the book chronicles the "seven days" as Lyman and co. scramble to stop the coup.