In essence, the play is a farce, full of misunderstandings.
Warning:wikipedia contains spoilers
The hero is Charles Marlow, a wealthy young man who is being forced by his family to consider a potential bride whom he has never met. He is anxious about meeting her, because he suffers from shyness and can only behave naturally with women of a lower class. He sets out with a friend to travel to the home of his prospective in-laws, the Hardcastles, but they become lost on the road.
While the bride-to-be is awaiting his arrival, her half-brother, Tony Lumpkin (one of literature's great comic characters), while out riding, comes across the two strangers, and, realising their identity, plays a practical joke by telling them that they are a long way from their destination and will have to stay overnight at an inn. The "inn" he directs them to is in fact the home of his parents. When they arrive, their hosts, who have been expecting them, go out of their way to make them welcome. However, the two men, believing themselves in a hostelry, behave rudely.
Meanwhile, Tony's sister, Kate, learning of the error and also acquainted with her suitor's shyness, masquerades as a serving-maid in order to get to know him. He falls in love with her and plans to elope with her. Needless to say, all misunderstandings are sorted out in the end, and Charles and Kate live happily ever after.