Should Scottish Opera be raising a toast to their new season, it would be no surprise to find Veuve Clicquot as first choice for bubbly. Why not another young widow at a party that already has two plus a merry one top of the guest list? Franz Lehar’s sparkly operetta The Merry Widow makes no less that 25 appearances touring Scotland this autumn, but it is Smetana’s rarely performed The Two Widows that takes pride of place amongst operas on the main stage in a new co-production with the Edinburgh International Festival.

Described by Francesco Corti, the company’s music director - who is conducting Scottish Opera for the first time since his appointment in 2007 - as an opera where there is, ‘not a word or a note too many and every phrase is perfectly formed’, The Two Widows is one of eight operas composed by the Bohemian Smetana. Very much the father figure of Czech classical music, he was dedicated to creating a distinct national style for that nation’s opera, his Bartered Bride being the best known result. Why The Two Widows, which looks to a French farce of the same name as its starting point, is so much less familiar is inexplicable. Scottish Opera has staged it once before, coincidentally enough at another Scotland-based festival, in Perth, prior to being part of its regular season in 1980.

It’s a fairly light comedy, catering for the general public’s desire in the 1870s for a happy ending. Not that true life, as ever, followed suit. In the same year that The Two Widows was premiered, Smetana discovered the first signs of syphilis, to lead soon after to total deafness, serious mental illness and early death. Sung in English, with a typically witty translation by David Pountney - who was director of the earlier production - the opera tells the story of two late 19th century Czech widows from the landed gentry and a bit of gentle manipulation towards remarriage for one of them. The cast is headed up by the young Scottish soprano, Kate Valentine, and the internationally renowned mezzo, Jane Irwin.

For 31-year-old Valentine, who was one of the stars of Scottish Opera’s innovative Five:15 new operas project earlier this year, it’s a major step in a rapidly escalating career. ‘Karolina is my first principal role on the main stage,’ she says, ‘and at the Edinburgh International Festival, it’s a big deal.’ As well as the Five:15, Valentine has covered Alice Ford in Falstaff and Constanze in last season’s Seraglio, where she came to the attention of the Two Widows directing partnership of Tobias Hoheisel and Imogen Kogge. ‘Scottish Opera have been fantastic to me,’ she says. ‘They get a lot of flak for not using Scottish singers, but I’m living proof that they do.’

Valentine’s character is full of optimism, hope and a general love of life. ‘She wants that for Anna too,’ she explains, ‘and to help her find happiness again, she engineers a plan.’ A mischievous game of love and jealousy pays off. ‘The characters are going through very real human emotions, so we need to take care not to be too frothy. Some of the music is heartstoppingly beautiful and really transports you from something that is folk-inspired to something quite a bit deeper.’

Irwin, in contrast to Valentine, is no stranger to the Edinburgh Festival. ‘I’ve sung in Edinburgh for the past 15 years with just one gap, for Bayreuth. I find it incredibly stimulating and the Festival tends to bring out the best in me.’ The role of Anna, who buries herself in the past and refuses to open up to her true feelings of love for an old flame, is the slightly more substantial of the two. ‘It’s a very large role in terms of stamina and a lot to memorise. There’s one huge aria, which I would call a “stream of consciousness” aria, where Anna pours out her emotions. The opera is really fun, but not all a romp and there are some very serious and beautiful moments in the score. There are definitely echoes of Czech folksong and although it is written with a Czech nationalistic streak, there is also the contrast between peasantry and the more monied society.’

It is the sort of opera that marks a new departure from the usual for Irwin who is a renowned Wagnerian interpreter including Brangäne in Tristan and Isolde with the Bamberg Symphony Orchestra for the Festival in 2005 and Waltraute in Scottish Opera’s hugely successful Ring Cycle, first seen at the EIF in 2003. ‘Now, I find I’m a romantic lead, dancing a polka! But there’s no reason why I can’t play a love-struck, young widow. For once, I might even get a decent frock to wear.’

The two young widows are close friends, having been brought up together since children. Karolina has always joked and teased her more contemplative cousin. Irwin and Valentine may not have quite that relationship but they have, as it happens, known each other for a number of years. After completing an undergraduate degree at the RSAMD, Valentine felt she was still too young for post-grad studies, so took a few years out to work in the travel industry. There was then a possibility that singing as a career might not happen. A chance contact led to Irwin hearing her and, says Valentine, ‘she gave me some lessons and inspired me to sing again. It is really special to be doing my first main role with Jane Irwin. She is very supportive as well as being a superb performer.’

Irwin realised Valentine’s potential straight away. ‘As soon as I heard her, it was very clear that she not only has a fabulous voice, but also a strong, innate musicality. It’s very rare that you get that combination of musicianship and voice.’ The pair also clicked on a personal level, and if it hadn’t been for Irwin, Valentine feels it would have been unlikely that she would be singing now. She was also fortunate enough to have encouragement at school, Grange Academy in East Ayrshire, where a particularly astute music teacher suggested that she might like to take singing onto further education. At that point, Valentine didn’t even know you could study music at college.

The raw talent that entered the RSAMD at age 18 is now a polished young professional who is looking forward to singing The Magic Flute’s First Lady with English National Opera next year and taking the Five:15 to the Tête a Tête Opera Festival in London immediately after The Two Widows. Contemplating her busy schedule, Valentine says philosophically, ‘well, it’s good to gather a bit of momentum at my stage, and although I’m going to need a holiday by the end of August, right now I’m getting my head down and enjoying the ride.’

It is the sort of rollercoaster ride that Irwin has been at the head of since winning the 1991 Decca Kathleen Ferrier Prize and it’s not one that either singer is likely to fall off. ‘I always wondered when the time would come that I would sing with one of my students’, says Irwin. ‘It’s fabulous that it is now happening, and Kate and I are working together as two singers on an equal footing.’

The Two Widows, Edinburgh Festival Theatre, Nicolson Street, 0131 473 2000, 9, 11 & 12 Aug, 7.15pm, £14-£64.