A professor of history at the U.S. Naval Academy and a former Marine, Jack Ryan is in London with his family researching a book. While dining in a restaurant, the Ryans find themselves in the middle of an assassination attempt by the ULA, a violent Irish terrorist group. Jack's old instincts kick in, and he manages to thwart the criminals and save their intended targets: the British Royal family. Lauded by the British and the Americans, Jack is invited to join the CIA. Meanwhile, the ULA have sworn vengeance against him.