The cast can undoubtedly be described as world-class. Constantine says a third of all professional stage performers in Britain applied for the auditions, which means the 30 cast members were picked from more than 3,000 applicants.

The two lead roles – originally played on Broadway by Idina Menzel (best known for her runaway hit Let It Go from the 2013 Disney animation Frozen) and Kristin Chenoweth – went to Jacqueline Hughes (Elphaba) and Carly Anderson (Glinda).

“Elphaba is very misunderstood; she’s humorous, witty and she’s very hot-headed, a bit like myself. But it’s such a beautiful story to tell, the challenges she faces and combats every time,” says Hughes, whose green-faced character rises above discrimination and rejection, and connects with anyone who has ever struggled with being different.

The heavy message, however, is delivered in a light-hearted way, and the story is punctuated with witty punchlines.

“That’s what I love about Wicked. There’s always something to see. I was a swing [understudy] in the show five years ago. So I got to watch it constantly, and every day I would be laughing at something different,” the performer says. “We never play for comedy, but naturally, our characters have found this comedic layer.”

Wicked became an instant hit after debuting at Broadway’s Gershwin Theatre in 2003, and grabbed three Tony Awards and seven Drama Desks Awards the following year. The musical has since toured through more than 100 cities and 14 countries, and opened in London’s West End in 2006, where it celebrated its 10th anniversary last month.

Adapted for the stage by Winnie Holzman, the musical is based on Gregory Maguire’s 1995 novel Wicked: The Life and Times of the Wicked Witch of the West, a spin-off of the children’s fiction classic The Wonderful Wizard of Oz by American author L. Frank Baum.

Maguire chose not to focus on the childhood classic’s characters, such as Dorothy and her misfit travelling companions. Instead, focusing on the Wizard himself, along with the two witches.

As audiences of the musical discover, there is another side to the characters we thought we were familiar with – even the monkeys.

“The way the story is told is done in the best possible manner. If something is slightly changed, it’s only to make sure the storytelling is the strongest it can be,” says Constantine.

One theme of the musical – that of friendship, especially between the two strong women – can connect with the audience, she says.

“But the main story behind Wicked is that you can change something for good, one person can make a difference. Anybody has the chance to stand up and make a difference, even if it’s just a small one.”

The family-friendly musical has plenty of humour, but it’s not without touching moments. One comes at the end of the first act, when Elphaba decides to go her own way and belts out the popular number Defying Gravity.

“I remember sitting in the auditorium when I was 17 and crying my eyes out because I was so wowed by the scene,” says Anderson, who has performed major roles in musicals such as Sunset Boulevard, Xanadu and Sunny Afternoon.

Her own character, Glinda, perhaps triggers more sniggers than sniffles. “When we first meet her, she’s perceived as quite superficial, because she comes from such a privileged upbringing. And she’s fearful of Elphaba. And from that fear, she discriminates against her and is mean to her,” Anderson says.

“Glinda is extremely complex. She goes on a huge journey. You don’t really warm to her in the beginning. But it’s making the audience turn around and realise that she’s good.”

Audiences will see similar transformations – a revelation of their true personality – in all the other characters, such as Madame Morrible and the Wizard. The former is portrayed by Kim Ismay – who has appeared in Mamma Mia! and Sunset Boulevard – and the latter is reprised by Steven Pinder. Wicked also features Emily Shaw (who was in the original cast of Matilda), as Elphaba’s sister, Nessarose.

Part of the charm of this production is the chemistry between cast members – the affection shown on stage is not just an act, but also a genuine reflection of their offstage relationship. Hughes and Bradley Jaden, who plays Fiyero, for instance, went to the same drama school and have known each other for a decade.

What really bring the magical Land of Oz to life, though, are the sets and costumes, designed by Eugene Lee and Susan Hilferty.

As the story takes place in a fictional world ruled by a illusion-conjuring wizard, everything is slightly off in the Land of Oz. The entrancing set for Emerald City is a giant clock counting 13 hours; all the costumes are asymmetrical.

Hilferty’s Tony Award for best costume design is well deserved. The details on each costume are so meticulous, they are not only for show but also authenticity. Glinda’s inauguration dress has layers of sequins sewn by hand; the coats of the Royal Guards are thick and heavy to give them a burly look, and even the buttons are imprinted with personal symbols.

And while the lives of ordinary citizens in the Emerald City are of no interest or relevance to the broader plot, Hilferty gave them each a backstory and a personality around which to create unique costumes.

Another trick audiences will miss is the rapid costume changes. On stage, the musical moves swiftly from scene to scene, giving the illusion that there are dozens of actors. Truth is, the same actors play the monkeys, the citizens of Oz, the guards and students. So they only have seconds to switch roles; the quickest costume change takes just eight seconds.

While much of the action takes place on stage, down in the pit a 16-piece orchestra provides the live musical accompaniment.

“Musically, it’s incredibly complex,” says musical director Dave Rose, who times the tempo of the score so precisely that it fits exactly with the timing of the dialogue – sometimes down to a single word in a line.

“It’s not just pop songs thrown together. But every aspect of the music, from the big signature songs and numbers to the simplest little piece of musical underscoring that happens under a dialogue scene. It’s so carefully arranged and written so that the music exactly complements the character on stage.

“When it all works correctly, it is incredibly rewarding,” he says.

And so it will be for the whole audience.

Wicked, Lyric Theatre, Academy for Performing Arts, Dec 8-Jan 22, HK$445-HK$945, HK Ticketing. Inquiries: 3128 8288