Each of the three acts of Noises Off contains a performance of the first act of a play within a play, a poor farce called Nothing On. The three acts of Noises Off are each named "Act One" on the contents page of the script, though they are labelled normally in the body of the script; and the programme for Noises Off will include, provided by the author, a comprehensive programme for the Weston-super-Mare run of Nothing On, including spoof advertisements and acknowledgements to the providers of mysterious props that do not actually appear (e.g. stethoscope, hospital trolley, and straitjacket). Nothing is seen of the rest of Nothing On.
Nothing On is the type of play in which young girls run about in their underwear, old men drop their trousers, and many doors continually bang open and shut. It is set in "a delightful 16th-century posset mill", modernised by the current owners and available to let while they are abroad; the fictional playwright is appropriately named Robin Housemonger.
Act One is set at the dress rehearsal at the (fictional) Grand Theatre in Weston-super-Mare; the cast are hopelessly unready, and baffled by entrances and exits, missed cues, missed lines, and bothersome props, including several plates of sardines.
Act Two shows a Wednesday matinée performance one month later, at the (again fictional) Theatre Royal in Ashton-under-Lyne. In this act, the play is seen from backstage, providing a view that emphasises the deteriorating relationships between the cast that lead to offstage shenanigans and onstage bedlam. The play falls into disorder before the curtain falls.
In Act Three, we see a performance near the end of the ten-week run, at the (still fictional) Municipal Theatre in Stockton-on-Tees, when personal friction has continued to increase. The actors remain determined at all costs to cover up the mounting series of mishaps, but it is not long before the plot has to be abandoned entirely and the more coherent characters are obliged to take a lead in ad-libbing somehow towards some sort of end.
Much of the comedy emerges from the subtle variations in each version as character flaws play off each other off-stage to undermine on-stage performance, with a great deal of slapstick. The contrast between players' on-stage and off-stage personalities is also a source of comic dissonance.