Mackenzie Allen, who serves as Vice President of the United States, has a tough decision to make, whether or not to go against the wishes of the dying current President. He has asked her to step down and let someone a little more appropriate take his place in the Oval Office. However, it's not only the President that is calling for her resignation, it's her entire party which elected her as the Vice President to start with.
As Mackenzie begins the transition into the office of President, she has to select a Vice President, a situation in which Nathan Templeton tries using to his advantage. Mackenzie's daughter, Rebecca, faces a crisis when her diary goes missing, which contains information about her mother that could hurt her.
Faced with her first national crisis - the death of nine DEA agents in Latin America - Mackenzie shows strength and resolve in dealing with a corrupt leader. Meanwhile, Nathan Templeton is approached by an ambitious congressman who served with Mac's Vice Presidential candidate, Warren Keaton, and is eager to divulge potentially damaging info in an effort to derail his nomination. Mac's teenage twins resume public school, only this time it's complete with secret service detail and press spectacle, and while popular Horace welcomes the attention, shy Rebecca finds it overwhelming.
All eyes are on Mackenzie Allen as she hosts her first official summit with the Russian President -- which is threatened to be overshadowed by Nathan Templeton's plan to engineer a series of cabinet resignations to coincide with the summit. Templeton goes after Mac with a vengeance, vowing to run - and win - against her in the next presidential election. Meanwhile, as First Gentleman, Rod must host his first state dinner for the Russian President and his wife.
In the middle of the announcement of her new National Security Advisor, Anthony Prado, Mac is caught off guard by the breaking news of a terrorist smuggling explosives across the Canadian border. The way in which Mac and her Attorney General deal with the situation pits them squarely against each other, and Nathan Templeton takes great pleasure in publicly second-guessing Mac's every move. Meanwhile, it's Halloween, and Amy - who desperately wants to go trick-or-treating like a normal kid - is disappointed to learn that, due to security concerns, she may have to settle for a party this year instead. When Rod as First Gentleman finds himself fodder for late-night comics, it hits his son Horace especially hard.
When a destructive hurricane hits Florida, Mac and Templeton fly to Florida to survey the damage. While there, Mac learns of an emergency situation with an oil tanker off the Florida coast which could have devastating consequences. Meanwhile, Rod is seriously considering an offer to become Commissioner of Baseball.
While trying to coordinate the rescue of the crew of a damaged U.S. submarine off the coast of North Korea with help from Chinese, Mac must deal with war fever among her advisors and a leak from China to the North Korean government that threatens to start a nuclear war. Meanwhile, Speaker Templeton’s wife secretly encourages Jayne Murray to accept Nathan’s offer to rejoin his office as chief of Staff.
While Mac is busy working on her first State of the Union address, Rod becomes a tad tipsy and is found in compromising position with an intern for all the world to see. Meanwhile, Templeton sets out to find a way to sabotage Mac's Homeless Initiative Bill. Plus, Dickie and Jayne, who has gone back to being Templeton's chief-of-staff, go out on a dinner date.
Mac decides to stand by her friend and Attorney General nominee, Carl Brantley, after he gets hammered in his confirmation hearings. A cargo plane which contains military weapons goes missing over Pakistan and it's up to Vice President Keaton to resolve the situation. Meanwhile, Rod tries to settle in the domestic life, but soon faces a crisis when Kate is nowhere to be found.
Mac wants her Attorney General to look into an urban situation in Maryland because it's where Gardner is from. Mac is also briefed on the situation of the missing surface-to-air missiles that went down in a military plane crash over Pakistan and has to make sure that the weapons do not end up in the hands of terrorists. Templeton is ralling support for the Templeton Act which focuses on domestic crime and Mac is threatening to use her veto power in the hopes for more law enforcement and education over the bill's calls for tougher sentencing. Dickie learns that Vince is planning a commitment ceremony with his partner and he warns him not to invite Mac because it might hurt her in the polls.
Mac suffers a burst appendix while aboard Air Force One. Since there is no Vice President in place, Templeton becomes acting President since he is the Speaker of the House and next in line. Meanwhile, there is an air strike that is crippling travel on Memorial Day weekend and Templeton ends up overstepping his bounds and handles the situation the way he wants to.
On Mac's birthday, she is faced with the fact that there are American hostages being held in Turkey by a militant Kurdish group. Meanwhile, she also has to interview new candidates to be her Vice President and Dickie tries to convince her of the type of person she needs to choose because her choice will affect her re-election campaign.
After a critic of the Equal Rights Amendment passes away and his wife takes over his seat, Mac believes she can amend the Constitution and pass the ERA once and for all. Meanwhile Templeton turns a Get Out the Vote campaign meeting into a presidential debate, Rod is asked to write a story about his relationship with Mac, and Rebecca finally learns the identity of her IM buddy, and both are shocked at just who the other person is.