Tom Kirkman is watching the State of the Union address in a conference room somewhere in Washington when his wife comes in. She's on the phone with their young daughter who hasn't gone to sleep for the night. Tom talks to Penny and convinces her to go to sleep. After they hang up, the screen blanks out, but all the other channels work. There's some commotion and a Mike Ritter, a Secret Service agent comes charging in. Tom goes to the window and sees the capitol is destroyed.
Flashback to 15 hours earlier. Tom and Alex are in bed being playful when their daughter interrupts. She wants breakfast, so Tom gets up to make breakfast which he apparently isn't very good at. He wants his older son, Leo to watch Penny later, but he is going to a friend's house. Alex leaves for work. Tom is walking to his office with his chief of staff, Emily who tells him that the president cut out all of his housing initiatives in the the State of the Union speech. Neither are happy and they go to meet with the president's chief of staff who tells Kirkman that he's basically fired by offering him a position as an ambassador to a nothing organization.
At home, Alex wants him to fight, but Tom is unsure. He gets a call that he's going to be the designated survivor for the evening.
Jump to present and Alex and Tom are being rushed into a limo. Mike gets a call that everyone at the president and most of congress was killed. He tells Tom that he is now the president.
FBI Agent Hannah Wells is at a bar watching the news coverage of the attack and tries to call her boyfriend, Scott who isn't answering when she gets a call from the director calling her into work.
Aaron, the deputy chief of staff, takes Tom to the Presidential Emergency Operation Center as Alex is taken to the residence. At the PEOC, Tom tries to get everyone's attention, but fails. Aaron does it for him, and Tom is given an update on what they know so far.
Overwhelmed, Tom leaves and heads to the bathroom where he throws up. Speechwriter Seth is in the bathroom too and starts slamming Tom, not knowing it's Tom in the stall next to him. When they both get out of the stall, Seth realizes who he's been talking to and apologizes. Tom tells him for now he's all they've got and tells Seth to get going on writing a speech for him.
Penny arrives at the White House and is greeted by Alex.
Hannah arrives at the disaster zone, but Jason, the assistant FBI director isn't too happy to see her. She convinces him why she should be allowed on the field and he lets her stay. He assigns Nolan and Lawrence to work with her. She looks a bit overwhelmed as she surveys the disaster in front of her.
Tom is getting some air when Alex joins him. He questions whether he should be doing this or not when Mike comes out to tell them they can't find Leo, but they are still searching for him. They go back inside when Aaron takes the president to another room where he's given information about the nuclear football.
Mike finds Leo at a club where he's selling drugs and takes him to teh White House.
Emily is trying to get into the White House, but is not being allowed in.
In another office, Tom, Seth, and Alex are discussing the speech when Aaron comes in to take Tom back to the PEOC. General Cochrane wants to start a war because Iran is moving warships into the gulf area which he thinks is taking advantage of the situation. Tom is unsure because no one has taken blame for the attack yet. He says he wants to meet with the Iranian ambassador before making any decisions, though he tells Cochrane to scramble his troops just in case.
A bomb squad detonates a bomb found in the rubble.
Kirkman meets with the Iranian ambassador and gives him three hours to move his warships out of the Gulf.
Nolan and Lawrence tell Hannah the bomb they found was one used by Jihadists who they think are behind the Capitol attack, but Hannah doesn't think so and that she doesn't think the attacks are done yet.
While Tom is getting ready to talk to the American people, Cochrane is outside with Aaron talking about removing Tom from office. Back inside, Tom starts to address the American people.