“Oh, she’s evil”, chuckles Arbroath’s number one mezzo soprano Karen Cargill. We’re discussing her brief but brutal appearance in Scottish Opera’s forthcoming new production of Puccini’s operatic trilogy Il trittico. In the central one-acter, Suor Angelica, Cargill’s coldhearted Princess coldly informs her niece – the eponymous heroine, who has been despatched to a convent and shunned by her aristocratic family for having spawned an illegitimate baby – that her child is now dead.

“I’m just there for that little nugget right in the middle of everybody’s night, an incredible ten minutes of raw, concentrated drama,” explains the internationally-acclaimed star, whose melting vocal versatility has graced the world’s most celebrated opera houses from the New York Met and London’s Covent Garden to Deutsche Opera; and who, as a consummate concert soloist, has made headlines with top-ranking orchestras from Berlin to Boston.

Does she feel in any way short-changed in this latest role? “Not on your life,” she fires back. “I get to make this dramatic entrance through the double doors. It’s my Norma Desmond moment!”

In reality, Cargill is one of the most unassuming divas in the business, generous professionally and personally, and infectiously cheery. And she is full of admiration for all around her, not least the South Korean soprano Sunyoung Seo who, in her Scottish Opera debut, plays the hapless Angelica.

“Sunyoung’s character is so vivid, you fall in love with it within seconds,” she says. “The voice is beautiful, and the combination of her characterisation and her music-making is wow – really wow. I’d never worked with her before, but when we first sang it through in rehearsal, it was really difficult not to just give her a big hug.”

Another target of her admiration is stage director Sir David McVicar. Despite his stream of five-star hits for Scottish Opera over the years, this is the first time Cargill has worked with him. “I’ve always been a huge admirer of David’s work, we know each other, and there have been possibilities that never quite happened in the past,” she says. “Watching his amazing [2008] La Traviata was a seminal moment for me. You felt you were experiencing real human beings, that you knew the characters intimately. That’s his genius. It’s true storytelling, and he knows the music back to front.”

Either side of the grim and shadowy Suor Angelica in Puccini’s trilogy are the tempestuous Il tabarro (The Cloak) and the riotously entertaining Gianni Schicchi, with its show-stopping aria, O! mio bambino caro. Understandably, her focus has mostly been centred on her bad news role in the trilogy’s centrepiece opera, but she also has an eye on the bigger picture: “I’ll be watching the floor run of the other two pieces,” she says, “to get a sense of how the entire evening hangs together.”

Followers of Cargill’s prolific career may have noticed a subtle shift in priorities, one deliberately geared towards balancing work with family life – she has a 14-year-old son “who’s obsessed with basketball and Metallica” – and is keen to share the fruits of her experiences with her pupils as associate artist of her alma mater, the Royal Conservatoire of Scotland.

“Choice is important,” she says, conscious that nowadays she has the luxury of being able to pick and choose more freely. Orchestral work remains her first love, having just performed Berlioz’s The Damnation of Faust and Schoenberg’s Gurrelieder with Edward Gardner and the LPO.

“I’ve never wanted to do too much back-to-back opera because I like to be at home as much as I can”, she says. That hasn’t stopped her committing this season to singing Mother Marie in Glyndebourne’s Dialogues des Carmélites with Robin Ticciati, however, or being part of last year’s Grammy-nominated recording of the same opera with the New York Met.

Nor does it diminish the loyalty she feels for Scottish Opera. “It’s my spiritual home, it’s where I started and where my teacher Pat Hay started. It always feels like an incredibly special place to be.” Even, it seems, when cast as the harbinger of doom.

Scottish Opera’s new production of Puccini’s Il trittico is at the Theatre Royal Glasgow, 11, 15 & 18 March and Edinburgh Festival Theatre, 22 & 25 March, www.scottishopera.org.uk

Karen Cargill: ‘Scottish Opera always feels like an incredibly special place to be’