If you can see most of the audience on their feet and bopping to music with huge grins on their faces, you can be pretty certain that a musical has hit the spot.
That was the scene in the Derngate auditorium at the end Hairspray, the feelgood phenomenon that lifts you up from the first notes and holds you right there until the end.
The new production of the international smash hit comedy/musical is set in Baltimore in the United States where it is 1962 and teenagers are hooked on a dance-based TV programme, The Corny Collins Show.
Tracey Turnblad (Freya Sutton) is a big fan in more ways than one and dreams of being on ‘The Council’, the gang of dancers on the show.
But just as her wish is realised, the teenager soon sees she must take a stand against racist attitudes of the producers.
All of that sound more serious than it actually is. The race issue is dealt with with the lightest of touches and doesn’t go beyond the basics of ‘integration: right, segregation: wrong’.
But that is not really a criticism. Hairspray takes the approach of showing the raw energy and sheer fun to be had when black and white dancers combine.
To that end, the main cast and ensemble were terrific.
Freya Sutton was the perfect kind of bubbly that the lead role needs and had a completely infectious presence, making an instant connection with the audience.
Her straightforward view of right and wrong and naive hopes were endearing rather than irritating and every single person in the auditorium was rooting for her in her quest to woo the star dancer on the TV show.
The jokes may have been occasionally lost on the audience, but the comic acting on the other hand, never failed to bring a smile. Tony Maudsley playing a cross-gender role of Tracey’s mum brought the best of a panto dame and gave it a dollp of camp US attitude.
Her dance number with former Blue Peter action man Peter Duncan was both funny and unexpectedly touching, and was a tribute to their sense of timing.
But it was the upbeat songs and dances that set the auditorium on fire with pure joy.
Good Morning Baltimore was an early highlight and the standard barely dropped.
The empowering ‘Big, Blond and Beautiful’ by The X Factor’s Brenda Edwards shook the very foundations of theatre with her immense soul voice, pushing her ahead as the best vocal performance.
And by the time of the finale of the iconic ‘Can’t Stop the Beat’, nobody wanted to see the end.
Just about everyone was standing, singing and dancing.
Any musical that can induce that sort of feelgood atmosphere is surely worth the price of a ticket.
Hairspray is on tour and is at the Royal & Derngate, Northampton, until October 3.
Box office details: 01604 624811 or BoxOffice@royalandderngate.co.uk