Was there anything in the script for tonight's episode that surprised you?
"The ultimate reveal, which is so critical to this episode of Peter. And that Walter really did intend to take the child back, that he only went over because Walternet had missed the cure. That was a surprise, and a wonderful surprise to me because I hadn’t realised that he had only gone across there because he had to, because otherwise the boy would die. That was a major reveal to me, and I think it adds a whole new light to the relationship between Peter, Elizabeth and Walter going forward."
When will Peter himself find out the whole story?
"We have eight fabulous episodes left and during the course of that, there will be a build-over of several of those episodes to Peter finding out. He does, in turn, find out - and that really dictates what happens in the last few episodes."
How does tonight's episode lead up to the season finale?
"It tells us why Peter is where he is and explains more of Walter's actions. We know that Olivia knows he's from somewhere else, so there's a build up to Peter finding out. Finally, he finds out and we literally tumble into these last two or three episodes. The finale is the big confrontation we've been promising for these last two years. All the things people have been asking for, we're going to deliver."
If Olivia hadn't seen the alternate universe, would Walter have told Peter the truth?
"I think inevitably the truth would have had to have come out. The escalation had started, so eventually he had to find out. It's much more interesting for him to find out through the wonderful character of Olivia."
When Peter discovers the truth, how does it affect his relationships with Olivia and Walter?
"It's very clear that we've created a hornet's nest. When Peter finds out, he is extremely wounded and outraged and bewildered and humiliated. Having finally found some trust in these two people, he is wounded yet again - and Joshua Jackson plays it beautifully. A relationship will be rekindled between Peter and Walter, but it will be different. There's a hint of this in the finale. Similarly with Olivia - their relationship with survive this breach of trust. It's far deeper than a romantic relationship."
It seems like Nina and Walter share a bond over Peter. Will that be explored this season?
"That will remain unexplored. It's something that won't be revealed in this set of episodes. It will come out next season, I believe. I know they have worked out what it is, but they haven't told me yet."
You're doing a musical episode. Have you - or any of the Fringe cast - had experience in musicals before?
"I did some in the early days. I certainly did some music theater, and I even dropped into a couple of operas in small-acting roles. We realise now that Anna Torv has got a beautiful voice, and that is just the starting point, you know. Jasika Nicole is also from a musical background. So, it was quite a reveal to us how much talent there was within the company. I was certainly not the A-lister in that group of people!"
Finally, do you know what's to come in season three?
"I asked the showrunner if he had a bible of stories, but he just said it's all in his head! I do know that there will be substantial time spent on the other universe, and when you get to the finale you will see why we have to do that. So, we will have this whole other universe playing in with this, at least for the first third of the season. That is all I can tell you at this stage."
Fringe continues tonight at 9pm on Fox in the US and Tuesday at 10pm on Sky1 in the UK.