How was it for you? Hiding in the wings: When it comes to prima donnas, two into one won't go

'IT'S bloody ridiculous]' a man yelled down from the gods at Covent Garden, halfway through Saturday's performance of Madama Butterfly. The audience was riveted; most people had probably never heard a heckler at the Royal Opera House before.

'Get her to put on the costume and do the part properly]' The woman he was referring to was Katerina Kudriavchenko, called in during Act 2 to sing the leading role from the wings, while Diana Soviero, stricken with a throat infection, continued to act the part on stage. Other members of the audience joined in the shouting; small phalanxes of staff ran around nervously. The conductor, Carlo Rizzi, declined to turn round. Lifting his baton, he continued to lead the orchestra through Puccini's opera.

In his dressing-room afterwards, Rizzi said he would have liked to have answered the heckler. 'I wanted to tell him to shut up. Can he foretell illness? Did he have a better solution? This was all we could do.' Admittedly, it was perhaps not the best night for an on-stage change of cast. As well as playing to a full house, the opera was being transmitted live on Radio 3.

'Tonight was a big strain for my nerves.' Rizzi revealed. 'Butterfly was not on top form; she was singing in different tempi. Sometimes she was slightly faster, sometimes slower, or short of breath.

'I felt her changing in almost every phrase; and I have to get the orchestra to follow her tempo. Then suddenly, mid-way through Act 2, with no warning, this new soprano comes on from the wings, and starts singing. It was very brave of her to come on at such short notice; but, at one point, both she and Soviero were singing; I didn't know who to follow. That was the worst moment of the evening. I have never before had a change of cast in the middle of a performance; and you see, this is Covent Garden, with 1,000 people. It's not easy. However, I know the score very well, and I could see that the new soprano knew the score, so once they sorted out who was singing, I realised we would be all right.

'What the audience probably did not realise is that, for Soviero to stop singing, here and before a live Radio 3 audience, she must have really been in pain. Butterfly is such a demanding role; the problem was not in her top notes, but in her middle range. The power had gone, she could not support the voice.'

Conductor of the Welsh National Opera, Rizzi was heading back home to Cardiff after a brief wash and change into T-shirt and jeans. 'Do I feel happy after tonight? Yes, quite. These things happen, you know. The best moment for me was in the Preludio to Act 3. The orchestra did a fantastic piano, with a beautiful sound that they have never done before. It was very . . . wrapping, enveloping. At that moment, I thought, I have actually achieved something with them tonight.'

Diana Soviero is scheduled to sing Madama Butterfly at the Royal Opera House tonight and Saturday (071-240 1911)