New York City in 1898 is the setting for Hello, Dolly!. Dolly Levi widow of Ephraim Levi, is on her way to Yonkers, New York to arrange the second marriage of the well known half-a-millionaire, Mr Horace Vandergelder. Actually she intends to marry him herself!

In Yonkers we meet Horace Vandergelder; his clerks, Cornelius Hackl and Barnaby Tucker and his niece Ermengarde. Dolly arrives in Yonkers and makes it her business to clear the field of all rivals including Mrs Irene Molloy, a young widow whom she herself presented to Vandergelder as a great catch - an heiress - whom he will meet when he marches in the 14th Street Association Parade. Vandergelder agrees and leaves for New York on business. Meanwhile his two clerks decide they have got some living to do before it is too late and plan to go to New York also.

Once more in New York we meet Mrs Molloy the young widow, whom Vandergelder has been considering as a possible second wife. With her in her shop is her assistant Minnie Fay and Dolly.

By chance, Cornelius and Barnaby take refuge in her shop to avoid meeting Vandergelder and are forced to hide in cupboards and under tables, whilst the ladies try to distract Vandergelder from finding them. Despite their best efforts, Vandergelder discovers that there are men in the shop, but doesn't know who they are, and is so angry he breaks off relations with Mrs Molloy and informs Mrs Levi that he will meet her 'heiress' at the grand parade.

Mrs Molloy is furious and Dolly tries to patch things up by arranging for Cornelius and Barnaby to take Mrs Molloy and Minnie Fay to dinner at the Harmonia Gardens Restaurant. Act II begins with Cornelius and Barnaby convincing Mrs Molloy and Minnie Fay that the really 'elegant' way to arrive at the Restaurant is to walk. Meanwhile, by 8 o'clock at the Harmonia Gardens Restaurant, the excitement reaches fever pitch as Mrs Levi makes a dramatic entrance. She pulls out all the stops to set about hooking Vandergelder. However Vandergelder discovers his two clerks and his niece are also there and discharges Cornelius on the spot. He is amazed to hear his once humble clerk unaffected and declare his love for Mrs Molloy in front of everyone.

Later in the prisoner's dock where Vandergelder has been taken for creating a disturbance at the Harmonia Gardens, he hears Dolly tell him the only thing she can say under the circumstances is 'So long Dearie'.

It is early next morning and we are back in Yonkers. Vandergelder, now without clerks, without his niece and without Dolly, realises he has been a fool and asks Dolly to forgive him and marry him!