I promised to update this blog if anything extraordinary happened on the show, and I have to say there was drama of a different and unexpected kind at Wicked this evening. All was going well on a two show day, and I was enjoying my usual chat with Andy Mace between my two scenes of the evening show when a tannoy call went out: "Would the company manager please come to the stage left wing immediately". Andy and I looked at each other with that naughty look that says "oh goody, there's going to be a drama!" Maybe I'm still a child but I always get excited when I sense something new is about to happen, and it is a most unusual call to put out. Once the show has started it is in the hands of the Deputy Stage Manager, Nick, who is vastly experienced and more than capable of handling on stage problems. For him to be calling in a higher authority means something major is going on. The company manager Wyn marches past and into the wing with a sense of purpose. A minute later he marches out with a sense of purpose that makes his first sense of purpose look like a stroll in the park. What can it be? And then we quickly remember, with a sinking feeling, that poor Idina was not feeling strong and was worried about herself vocally before the show. Could it be that she feels she can't go on? Surely not – Idina is a powerhouse; she's never, ever had a hint of tiredness or hoarseness, let alone a show off. But Wyn is heading for Wardrobe. This does not bode well. And then in a blur a "wiggie" (someone from the wig dept) comes running past. "Well that's that, then" says Andy. I look at him quizzically. "That was Kerry's wig that just went past us." Kerry is the standby Elphaba, and there can only be one reason to bring her wig down. Idina had done her best, but after an hour of Act One, and with the immensely challenging "Defying Gravity" looming, she had reluctantly decided to throw in the towel.

Suddenly it was all systems go. Impromptu meetings all over the place, and a plan of action quickly agreed and communicated to all depts. We will stop the show at the end of Emerald City as we go into the Wizard's Chamber, Wyn will make an announcement, and Kerry will take over. By the time we stopped, Kerry was in costume, fully greenified and in the starting blocks. To be suddenly on, mid way through Act One, and to have to make your debut in the role starting with Defying Gravity is a kind of "nought to sixty" experience that must be beyond terrifying, but Kerry had little time to contemplate it. It took a mere 90 seconds to transfer the mic packs so the new Elphaba mics (head mic, hat mic and back up mic) were on the right frequencies, and the show was back up and running. As she ran onto stage the wings were packed, the whole company willing her on, and craning to see and hear her. This sudden influx to the wings threatened to cause chaos for the stage crew, who still had all their normal cues to perform at a particularly busy section of the show. They had every right to simply say "clear the wing – we need to be able to work" but sweetly they totally understood how desperate everyone was to witness this bit of Wicked history being made, and they patiently picked their way round us with nothing more than the occasional "sorry guys, can I just squeeze through".

As Kerry ran on I tried to imagine how she must feel. She's been a part of the company since Day One, in every rehearsal, seen us all through the madness of that first preview, the terrors of Press night, and seen the company settle in to the rhythm of eight shows a week, all without actually sharing that journey with us on stage. She must be absolutely champing at the bit to get on and prove herself – to an audience, to us, to herself. And yet could this moment be more terrifying? To be thrown on suddenly, in the middle of an act, to sing one of the hardest, most exposing and technically demanding songs in the musical theatre repertoire? Frankly, I'd rather stick a hot poker down my willy. But Kerry is made of sterner stuff. In the wings she had been calm, focused and completely together. On stage she was now precise, truthful and instantly touching, and she pitched her performance at exactly the right place on the emotional arc of Elphaba's journey. And then it was Defying Gravity…

Now when you've only heard Idina sing it, both on the cast album and in the flesh, you can end up associating the song entirely with her, to the extent that you forget that anyone else might be capable of singing it. I must confess that without realising it, that's just what I had done. Till tonight. To listen to Kerry Ellis claiming the song for herself you would never believe that it was the first time she had sung it. It's not just that she sang it beautifully (of course she did, she's Kerry Ellis), but that she did so with such confidence, such style and such belief. She acted it, she committed to it and she SOLD it. And on the final black out at the end of Act One, the audience told her so.

There was such euphoria and enthusiasm from everyone at the end of the act that it was a moment before I realised that wasn't it - she still had Act Two to do! The change over had happened since my scenes with Elphaba so the first time I met Kerry on stage was in this second act. I looked up at this unfamiliar green face just as she says "Dr Dillamond, don't you recognise me?" And all I could think was "well frankly, no – I've never seen this green face before in my life!"

Kerry is a wonderful Elphaba, with a beautiful, beautiful voice and a lovely quality on stage. As I watched (and heard!) her triumphant reception at the curtain call I felt a delicious feeling of anticipation: come New Year I'll get to play this show with her for six and a half months! I am very pleased to be able to report that Wicked is in the best possible hands next year.

We all wish Idina well and all the best for a speedy recovery and a quick return to Oz.