After leaving her job with the Supreme Court in order to marry Phillip Manning, a Justice Department attorney, Mary Peppertree breaks their engagement and begins a new job as a telephone operator at the White House, where her father Timothy is a long-time guard. Her first call is from David Paxton, a fishing expert who rudely insists on speaking to the President. The remainder of her day is spent with various calls from Supreme Court justices, all attempting to reconcile her with Phillip. Later, Mary is confronted by Phillip, and she tells him that she broke their engagement not because she saw him with another woman, but because she was not jealous about it. Their conversation is overheard by David, who pledges to Mary that he will speak to the President, despite her interference. The next morning, David attempts to bribe Mary with flowers and candy, only to have them thrown back into his face. Later, after talking to a hiccuping Mary, the President sends Harvey Elwood, his executive secretary, down to the switchboard to check on her condition. As she is leaving work, Mary is forced to drive David off the White House grounds in order to stop his arrest, then agrees to let him speak to Elwood if he takes her to Supreme Court Justice Peabody's party that night. Lt. Tom Farrington, a naval aide at the White House, has been sent to escort Mary to the party, however, as the President had earlier overheard Mary telling Phillip that she would rather stay at home than attend the party with him. The next morning, the President learns that Mary is upset over breaking her date with David, so he calls the fishing expert himself to express his regrets. Later, Mary and David have lunch, and she arranges a meeting for him with Phillip. Tom then arrives at the Peppertree home with presidential orders to take Mary to a film screening at the White House. When Phillip learns that Mary is on a date with Tom, he has Justice Peabody call Elwood, who tells the justice that he and the President were merely trying to protect Mary from David. Phillip then questions David about his relationship with Mary, and the marine biologist announces that he is leaving town, as everyone in Washington seems to have a "Mary Peppertree fixation." Meanwhile, newspaper publisher Samuel Litchfield complains to Elwood about Tom's attentions to Mary, as Tom is also dating his daughter. After Elwood assures him that she is "practically engaged" to Phillip, Mary and Tom arrive together at the restaurant. In turn, Gustav Heindel, an immigrant restaurateur, tells Elwood that he saw Mary kissing David, so the presidential secretary decides to handle the matter with the Navy personally. Learning that this might keep David in Washington for another three weeks, Phillip offers to put the Justice Department on the case and promises to clear up the matter in two days. That night, upon Elwood's orders, David takes Mary out on a date in Tom's place. After kissing David, Mary realizes that she loves him, but when Phillip and Tom appear, David angrily leaves. After his departure, the other two suitors propose marriage. The next morning, Mary receives congratulations on her engagement to Phillip from the Supreme Court and congratulations on her engagement to Tom from the President. Meanwhile, Elwood learns that David is not technically a citizen of the United States, so he has the young man arrested for illegally entering the country. He soon discovers that the Pacific island on which David was born and holds a deed now houses a strategic military base, and if David is declared an alien, the Navy could be forced to move. After meeting with the President's advisors, David agrees to American annexation of his island if both Phillip and Tom are given appointments far from Washington, and both he and Gustav are made U.S. citizens. The government readily agrees, and when Mary calls the President with the good news, David interrupts her conversation with a kiss, causing both to break out in hiccups.