When a sudden explosion decimates the Capitol Building during the State of the Union address, Secretary of Housing and Urban Development Tom Kirkman is sworn in as President after learning that both his predecessor and fellow Cabinet members are dead. As he juggles adjusting to his new role and proving he is capable of leading the country, FBI agent Hannah Wells begins to suspect that the attack may be the first of many.
The episode opens with Tom Kirkman in an office building room near the Capitol building, watching the State of the Union address being delivered by President Richmond on TV broadcast. While chatting with his wife, and having just told his daughter good night on the phone, signal is abruptly lost to the Capitol. After others quickly affirm that signal to the address has been lost all around, his Secret Service agent, Mike Ritter, orders Kirkman to proceed to a safer location until more is known. Kirkman walks over to the office window, and upon opening it, he, his wife, and Ritter are aghast by the sight - a fireball rising above the Capitol building.
A flashback occurs, showing Kirkman waking up with his wife fifteen hours earlier. While attending a board meeting, he is confronted by the fact that Richmond does not intend to include Kirkman's topics in the State of the Union address. Later, when he gets home, Kirkman is notified that he will be the designated survivor during the address. As the scene ends, he asks what the Designated Survivor actually was.
Back in present time, Kirkman is escorted out of the building by a police and FBI caravan to the White House. While en route, Ritter informs him that the president and his entire cabinet have been killed in the attack on the Capitol, leaving Kirkman as the President of the United States. At the White House, he is quickly sworn into office and taken to an underground bunker. Here, Kirkman begins to discuss the situation with a team of other government officials. A general encourages a show of military force against Iran, which he believes is responsible for the attacks, and Kirkman is tempted to use the nuclear football. After a disagreement, Kirkman dismisses the room, saying, "We'll have it my way," but is still completely uncertain as to what course of action he will take.
A woman named Hannah Wells watched the breaking news coverage of the Capitol bombing. After a failed attempt to call her lover, Scott Wheeler, she got in her car and rushed to the Capitol. At the wreckage, the crews working uncovered an explosive device, but was deemed dysfunctional. Having her suspicions about the sudden appearance of the bomb, Hannah comes up with the theory that the perpetrators were not done with whatever they were planning.
Kirkman discussed the situation further with his wife and other members of the White House, and prepared for a speech he was planning to deliver to the American audiences. The episode ends as the cameraman for the speech counted down time to start.