Once Upon a Mattress was written and composed in 1959; its Broadway debut is what made Carol Burnett, as Princess Winnifred, famous.  The musical is a farce that takes place in the 1400's in an imaginary Kingdom. 
    The story is narrated by a Minstrel, who tells us that the tale of the "Princess and the Pea" is not quite like what all of us were led to believe.  He tells the real story:  By decree of the tyrant Queen, no one in the Kingdom is allowed to get married until a suitable wife if found for the young prince, Dauntless.  But the Queen, for various reasons, does not want Dauntless to be married.  For each princess candidate, she and the court Wizard devise impossible tests--tests to see if each Princess is good enough for her boy. 
    The reigning Knight of the Kingdom, Sir Harry, has gotten his amour, Lady Larken, pregnant.  If the court finds out, his career is doomed.  So Harry goes on a quest to find a princess who can pass muster, so that he and Larken can marry (as well as the rest of the couples in this Kingdom). 
    Meanwhile, the King--struck mute by a curse years ago--wanders the castle with his only friend, the Jester, chasing wenches, since he can find no fulfillment with his horrible wife. 
    Sir Harry returns with Princess Winnifred, a brash, wild, unkempt girl from the swamps.  She turns the kingdom upside down.  Worse yet, Dauntless and she fall in love!  (what a surprise...).  The Queen and Wizard frantically devise a completely unfair test to deny Winnifred her chances--hiding a pea under twenty mattresses.  If the pea does not keep her awake, she's no princess. 
    The Minstrel, Jester and King convince Harry to help them "cheat".  They schmooze with the Wizard who, it turns out, is lonely too, and he divulges the secret plan.  You'll have to come see it to learn how it ends.
    On its way to closure, the show features a host of outrageous musical numbers, including pantomime singing performances, sweet and elegaic love songs.