Performances at Cambridge Arts Theatre until Saturday (May 24).

Written by three members of this most athletic cast, The Play that Goes Wrong had the Cambridge Arts Theatre audience in hysterics from start to finish.

This is what happens, you see, when amateurs put on a murder mystery, with none of the props in the right place at the right time, (so the detective has to pick up a set of keys and a glass vase and pretend it’s a notebook and pen) with understudies who have to read their script and include the stage directions – and with actors who know their words by rote so that when something alters they blindly stick to the script however inappropriate it has just become. They are not “in the moment”.

Oh and there is the one where someone says a line too soon and the other person still says their next line anyway, because it’s their line even though now it makes no sense. So that you get: “Don’t tell me to calm down” followed by “calm down”.

The cast of the play within the play, The Murder at Haversham Manor haven’t listened to the whole play. They only know their cues so that if someone gets a line wrong, just before theirs, they have to keep repeating the lines until they can move on.

Actually, this is not just a dig at amateurs, this show is also a bit of a hymn to the fringe, where so many actors start. Audiences would be surprised how much of it actually happens out there. How many times actors invent lines to go off and bring someone on who has missed their cue because of the cheering at the football in the bar.

On the fringe, there’s no budget for anything – and the lovely touch in this play of being able to see “gents” written on the door when it swings open to the stately home drawing room, may be a fond allusion to how often you have to pass the open door of the gents as you go on stage at the back of a pub.

What had the audience falling apart was Nigel Hook’s ingeniously falling apart set. It really does look rickety and it disintegrates bit by bit. At one point two actors are trying to stay on a sloping floor, on an upper level high above the stage. It starts off horizontal and falls down by degrees till it is as shut as a garage door.

Threatening to collapse from the beginning, by the end whole walls have fallen down leaving the actors standing upright in what were once doors and windows like in the films of Buster Keaton.

There are clever surprises when people appear in unexpected places and one especially slick turn when a body is carried out on a stretcher which is merely two sticks – the fabric having been completely torn off in an earlier joke. The actor (dazzling Dave Hearn) just clings on to the two poles and is even able to be turned sideways through the door.

All the cast put their heart and soul into a comic gem, that would actually be very difficult to do (dare I say it) for the untrained. The apparent chaos in fact depends on immaculate timing, gymnastic litheness, having all the right props indeed in the right place and knowing the lines upside-down and backwards because that is how you are going to have to say them.

It’s not fair to pick anyone out, they are all great – but I did love Greg Tannahill’s dead body, which was obliged to move itself around the stage and even climb “discreetly” from one floor to the other. A performance surprisingly authoritative and authoritative in its surprises.

With no let up in the humour and fine performances in an ensemble piece directed by Mark Bell, this is a great night out. Once you have seen how it works, it might be a while before you take a play seriously again. You might want it to go wrong.