When Dorothy plummeted to earth and was handed those ruby red slippers with which to follow the Yellow Brick Road, she didn’t inquire too closely about their previous owner.

Who was the woman unceremoniously squashed beneath a random flying Kansas farmhouse?

In Wicked – the multi award-winning musical based on Gregory Maguire’s book The Life and Times of the Wicked Witch of the West – the audience finds out, along with a whole raft of other back-story details which will mean you never view the land of Oz in the same way again.

Emily Tierney and Ashleigh Gray star in touring production of Wicked (Photo credit: Matt Crockett)

Was Glinda really good? Was the Wicked Witch of the West all that wicked? What did the great Oz get up to behind his curtain in Emerald City? And how did the tin man lose his heart, the scarecrow be so scatty, and the lion become so cowardly?

“It’s actually quite a political piece,” says Liverpool actress Carina Gillespie, who plays Nessarose, the younger sister of Wicked’s bewitching green ‘heroine’ Elphaba in the touring production which arrives at the Liverpool Empire next week.

“There are lots of kind of jukebox-y musicals out there, and this is a musical that is so intelligent.

Steven Pinder stars in the touring production of Wicked (Photo credit: Matt Crockett)

“Every time you watch it you pick something else up from it. I’ve got family members that have been three, four times, and each time they go - ‘oh my goodness, I didn’t realise that was because of that’,’ or, ‘it’s really clever’.

“And it’s also really funny.”

Nessarose isn’t though, to be fair, what anyone would describe as a bundle of laughs. When the audience first meets her, the character is wheelchair-bound and “extremely spoilt”.

“She’s a troubled soul isn’t she?” Carina agrees. “It’s a very interesting character to play.

“She’s extremely volatile and not quite in control of her emotions, and of course just thinks that everything in her life, everything that doesn’t go right, is because of the fact that she’s disabled.

“So when Boq (one of the munchkins in Wicked) doesn’t love her back, she just thinks it’s because she’s in a wheelchair. Which is so heart-breaking.

“And of course it’s not. It’s because she’s not Glinda the Good.”

Samuel Edwards and Ashleigh Gray star in the touring production of Wicked (Photo credit: Matt Crockett)

The current Wicked tour started this time last year in Manchester, although Carina’s own entry was delayed by two months after she took a tumble on holiday and – ironically, given the role she was due to play – returned home in a wheelchair. She didn’t walk for five months.

“Just a bit of character research for Nessarose!” she can joke now, although it didn’t feel funny at the time.

Carina explains: “I was on holiday with my fiancé, and, ironically, celebrating getting this role. We were sightseeing up a mountain and I slipped, fell backwards, and broke both bones in my leg all the way through.

“That was a scary phone call to make when we got back. My agent luckily did it for me and kind of made a joke – ‘she’s just a method actress!’.”

Wicked is at the Empire from September 16-October 11. Call 0844 871 3017 or visit www.atgtickets.com/liverpool .