Kay Thorndyke is called to the home of her father, newspaper publisher Sam Thorndyke, who is dying.  A bitter old man, Sam recounts how the Republican Party betrayed him and that he would be dying in the White House if they had continued to support him.  He tells Kay how proud he is of her and her ruthlessness, and reminds her to "make heads roll."  After Kay leaves, Sam, tired of his suffering, kills himself.

Now the head of the Thorndyke Press, Kay begins the work of grooming her own man for the White House.  She meets with Jim Conover, a crusty, back-room political kingmaker somewhat out of favor with his party, and asks him to head the campaign of her handpicked candidate:  self-made aviation mogul Grant Matthews, "a rare combination of sincerity and drive that the common herd will go for."  Kay also brings in one of her columnists, "Spike" MacManus, a self-described "poor man's Drew Pearson," to be press secretary for Grant.

When Grant arrives in Washington, he feigns disinterest in running for president, arguing that he is not a "politician" but a plainspoken American.  Despite his honesty, however, Grant is also an ambitious man, which Jim quickly recognizes, and he agrees to test the idea by giving a number of political speeches as he tours the country visiting his airplane factories.  Jim tells him that rumors of an illicit relationship with Kay would ruin any chance for the presidency, so they must stop seeing each other.  Kay readily agrees, but Grant is reluctant, as he must ask his estranged wife Mary, an idealistic woman, to go on the speaking tour with him.

Later, when Jim and Kay are alone, he balks at the idea of running Grant's campaign, until Kay not only offers him the chairmanship of the Republican Party if Grant wins, but a Vice-Presidential position with the Thorndyke press, as well.  Most importantly, both agree that Grant is the type of man they can control.  When Mary first joins the campaign, she believes it is an attempt at reconciliation by Grant, but finding Kay's carefully placed glasses on Grant's nightstand, she decides to go home.  Learning that Grant is thinking of running for president, an idea she wholeheartedly supports, she then agrees to share the candidate's campaign, if not his bed.

While Jim works the political back rooms, making dirty deals in Grant's name, the speaking tour begins with great success.  Kay, on the offensive, fires the editors of her newspapers when they refuse to do "anything" to deadlock the Republican convention, Grant's best chance for the nomination.

In Wichita, Grant, under Mary's influence, makes his own controversial speech, instead of one of Spike's carefully prepared ones.  In Detroit, Grant plans another speech, this time attacking management, but Jim arrives and tells Grant such a speech will end his chances for the Presidency.  Grant is undeterred until he meets secretly with Kay and agrees to make the prepared speech.

After Detroit, Grant is a changed man, meeting with all the special interest groups that Jim brings to him and making any deal he can that will get him convention delegates.  To formally announce his presidential aspirations, Grant prepares an elaborate national broadcast from the Matthews' Long Island home.  To deflect rumors, Mary is forced to invite Kay to the broadcast, which is the same night as the Matthews' wedding anniversary.  When some of the politicians attempt to renegotiate their deals with Grant, Kay steps forward and shows that she is the real power behind the campaign.

Mary, finding out that Kay was in Detroit and realizing the role she has played in Grant's campaign, gets drunk and announces that she will not make her speech.  Kay quickly agrees to make the speech for her, while Spike warns Mary, whom he has come to admire, that if Kay gives the speech, she will lose Grant forever.  At the last moment, Mary steps up and begins the speech.  Grant, seeing how Mary's compromise of herself is a mirror of his own actions, can take no more.  He stops Mary and proceeds to attack all the politicians who supported him, saying that he is no better because he played both sides and lost his faith in both the people and himself.  After the speech, Grant and Mary reconcile, as Kay and Jim leave, looking for another "candidate."