The major device that sustains the tempo of the play is dramatic irony. Dramatic irony occurs when characters in the play are unaware of the consequences/ significance of their actions in the scheme of things, though, the audience is.
Young Marlow and Hastings, men of the world, are easily led by the joke of Tony into believing that they are in an inn when, in fact, they are in the house of the Hardcastles. Under this ironical impression, they consider Mr. Hardcastle as an inn keeper, his daughter a barmaid. The two are deceived about Kate. Thinking that they are, indeed, in an inn, the object of their visit, Kate, falls to the level of a mere maid at the inn and she is made to tolerate abuse, to the amusement of the audience. Hastings and Miss Neville's elopement plan hinges on her jewels for Hastings who hands them over to Marlow for safekeeping. Seeing that he has no safe place, he, in turn, hands the jewels over to Mrs. Hardcastle who has been looking for the lost gems. This is ironical, as, unknown to Marlow, he has just foiled Hasting's plans and rescued Mrs. Hardcasting from trouble from the trouble of losing Miss Neville's jewels.
Tony is at his pranks again when he rides Mrs. Hardcastle round about the vicinity, pretending to be heading for Aunt Pedigree's place. He dumps his mother in a bog and frightens her that robbers are in the area. The fact, however, as the audience is aware, is that they are not far from the Hardcastle home and there is no gang of thieves. Such use of dramatic irony creates amusing moments in the play.

Points to note:
(a) Dramatic irony occurs where characters in the play are unaware of the consequences/significance of their actions in the scheme of things, but the audience is.
(b) The expectation on the part of Marlow and Hastings that they are in an inn when, in fact, they are in the Hardcastle home.
(c) The deception on Marlow that Kate is a barmaid when, in fact, she is daughter to Mr. Hardcastle and his (Marlow's) future fiancee.
(d) The entrusting of the jewels in care of Marlow who presents it to Mrs. Hardcastle.
(e) Mrs. Hardcastle's believing that she is among a gang of thieves when in fact she has not moved far from home.