Kate Miller-Heidke is a multiple-ARIA-nominated singer-songwriter who successfully crosses genre lines between pop and opera. When she was asked to compose her first score, for the musical adaptation of Shaun Tan’s award-winning illustrated 1998 children’s book The Rabbits, showing at Sydney Festival in January, she admits to being stumped.

“The book contains only 12 sentences, and it’s a very simple story. At first I couldn’t envision turning it into an hour-long piece.” Miller-Heidke says.

The ideas began to flow the moment she met the show’s creative team: playwright and Belvoir favourite Lally Katz; designer Gabriela Tylesova (whose Sleeping Beauty with The Australian Ballet is currently playing at the Sydney Opera House); and respected theatre and opera director, John Sheedy, among others.

Tan and the The Rabbits’s author John Marsden gave the team free rein to develop the book’s ideas, which explore the colonisation of Australia and its impact on Indigenous Australia. In both the book and the musical these topics are dealt with in a deceptively picturesque, colourful fashion. Aborigines are depicted as marsupials, and the newcomers as rabbits.

The one-hour musical is a co-production by Opera Australia, West Australian Opera Company, Barking Gecko Theatre and the festivals of Perth, Melbourne and Sydney. Both Perth and Melbourne seasons were a critical and box-office success, selling out their houses. Now it’s Sydney’s turn.

Tylesova’s wildly imaginative sets and costumes, and Katz’s approachable libretto, make this a production that, while ostensibly for children, contains deeper layers of meaning for adults.

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“I had no interest in portraying a really blunt black-and-white story [but] it’s such an important story to tell,” says Miller-Heidke, who’s also the principal soprano in The Rabbits, playing the character of The Bird. “The rabbits sing in a Gilbert and Sullivan-esque style, the marsupials have a more pop-music-theatre way of singing, and the libretto is gorgeous and sparkly but not highly poetic, it’s humorous.”

Nevertheless she says the message of the damage wrought is never lost on the audience. “In Melbourne people stayed in their seats for several minutes afterwards, trying to process the emotion of it. And during the stolen-generations scene one night we had one kid say really loudly to his mum, ‘But they’re going to give the babies back, aren’t they mummy?’”

Seeing the finished production was one of the most rewarding experiences Miller-Heidke has had. “It’s always thrilling to see the completion of a big project like an album or a tour, but I’ve never had something of this scale come together – seeing my music and the costumes and the sets – it’s this huge operation and a really rewarding collaborative process.”

Since working on The Rabbits Miller-Heidke has turned her hand to other endeavours, many of them taking her further into unchartered territory.

She’s been busy “growing a beard downstairs for Christmas”, or so she sings in her newly released Christmas single with good mates The Beards. It’s a fund-raising effort for bowel cancer (which was picked up and retweeted by fan Amanda Palmer to her own 1 million-plus twitter followers as a tongue-in-cheek follow up to her own witty ditty Map of Tasmania).

Then there’s an upcoming show at the MONA FOMA festival in Tasmania; a new song for good friend Meow Meow’s Sydney Festival show – the decidedly un-Disney cabaret show Little Mermaid; a star turn in the free digital download The Book of Sand, a multi-layered “choose-your-own-adventure” interactive song cycle composed by Dutchman Michel van der Aa; and a recent new composition co-written and performed by Tina Arena for the ABC’s Q&A in support of White Ribbon Day.

“It’s all happening,” she laughs. “I do like to do a variety of diverse projects, I find it keeps me interested and challenged. I get quite bored doing the same thing over and over.”

The Rabbits plays at the Roslyn Packer Theatre January 14–24.

The Book of Sand is a free digital download, available now.

Kate Miller-Heidke tours capital cities and regional centres from February.