The Girl Who Came to Supper is set in 1911 London at the time of George V's coronation. The first Act opens with the finale of the 'play within a play 'The Coconut Girl' where the leading lady Jessie Maynard is singing about her complicated love life while sitting on a garden swing. The curtain falls and the cast gather backstage to meet a royal visitor, Grand Duke Charles, Prince Regent of Carpathia. Everyone falls at the feet of their visitor - except Mary Morgan who plays Jessie - who literally trips and falls into his arms. This provides the spark of interest the Prince develops in her and he sends Northbrook his assigned British diplomat to invite her to supper. Mary's head is turned and she imagines a future where she is the toast of society.
At the Carpathian Embassy the staff express their annoyance at the disruption the royal visit has made to their lives. The Prince worries about the news of civil unrest at home and a nervous Mary with her 'five and dime store' background feels ill-prepared for an evening with royalty.
The Prince has prepared an intimate dinner for two that he hopes will foster romance. The evening does not go well. Interruptions by the Queen Mother, a vague woman who mistakes Mary for a variety of people including Sarah Bernhardt and begs her son to be less hard on his son King Nicolas who has been supporting the Caropathian rebels. Phone calls interrupt on the political situation back home and the arrest of the rebel leader, that are complicated further by Mary imbibing too much and reciting the American Bill of Rights and the arrival of King Nicolas protesting about the treatment of his rebel friends. Northbrook arrives to save Mary from her fate and the Prince tries to arouse Mary's sympathy for his plight but to no avail as Mary has passed out!
Frustrated by events Nicolas storms out and walks the streets of London where he meets Ada Cockle a fish and chips seller with a homely line in philosophy. She belts out a selection of cockney songs to a crowd of like souls.
Mary and the Prince emerge in the morning - she being unsure of the events the night before presumes she has spent the night with the Prince and must be in love. The Prince's icy responses brings her back to earth and on Northbrook's arrival she becomes anxious to leave. She meets Nicolas on her way out who expresses his interest in her. Before she is able to leave Mary meets the Carpathian delegation in full regalia on their way to the Coronation. The Queen's lady-in-waiting is ill and she urges Mary to take her place. Before doing so she must be invested by the Prince with Carpathia's Order of Perseverance, awarded for 'personal sevices to the head of state.'
At Westminster Abbey the crowned heads and peers of numerous nations wait in boredom. Mary returns to the embassy to return her borrowed clothes and is persuaded by Nicolas to ring the German Amabassador to tell him of his plight. The call is interrupted by the Prince who places Nicolas under house arrest and castigates Mary for her complicity. True to her nature Mary rounds on the Prince before being dismissed. Left alone the Prince contemplates how this unusual woman has affected him. Mary convicnes the Prince to be a more loving father - Nicolas is released and ordered to the Foreign Office Ball. The Queen Mother commands Mary to accompany Nicolas. At the ball the guest 'get down' with a ragtime number and the Prince invites Lady Sunningdale to join him later for an intimate supper. He is pleased to meet a woman who knows the rules, unlike Mary. On their way home Mary and Nicolas relax and she tells him in song about the fantasy of the theatre world she inhabits. Back at the embassy - to return her borrowed jewels - realisation is on the horizon as Mary sees the supper setting and imagines the Prince hopes for a second engagement. The Prince decides to have his revenge and brings out the vodka. Mary produces a proclamation she has written for Nicolas that repudiates his alliance with the Germans and the rebels to overthrow his father. He expresses his admiration for this worthy adversary and admits his true feelings. The next morning the Prince is a new man - realisation has struck and he decides on free elections in Carpathia and asks Mary to return there with him. Nicolas is delighted at the changes and he and the Queen agree that Mary must visit his country. Mary knows that life is not like this. Regretfully the lovers part and the Prince realising that he cannot stand in the way of progress leaves. As the servants cover the furniture Mary looks around and picks up a single rose as a souvenir and quietly steals away.
The cast included Florence Henderson as Mary, José Ferrer as Charles, Irene Browne as the Queen Mother, Sean Scully as Nicholas, Tessie O'Shea as Ada Cockle, and Roderick Cook as Peter Northbrook.
Henderson and O'Shea were singled out for praise by the critics - the former for her one-woman delivery of an abridged version of The Coconut Girl, the latter for her extended song-and-dance routine - but the highly influential Walter Kerr's review was negative for the most part. He and others felt the show was an unsuccessful attempt to duplicate the success of the earlier My Fair Lady.
O'Shea won the Tony Award for Best Featured Actress in a Musical. Nominations went to Coward and Kurnitz for Best Author of a Musical and Irene Sharaff for Best Costume Design. The show proved to be the last with a Coward score and the only one of his musicals never produced in London.