Corrie fans were left dumbfounded on Friday when it emerged that Pat Phelan wasn’t a murderer after all – but a kidnapper.

Seven months after he disappeared, presumed dead after Phelan clouted him round the head with Kevin’s laptop, Andy Carver is alive and being held hostage in the basement of a derelict building by the evil builder.

[Related: Read the latest weekly Coronation Street spoilers]

Actor Oliver Farnworth tells us what it’s been like keeping such a big secret, how he prepared for the return to the soap and what’s next for both Phelan and Andy…

When did you find out that this was the plan?

I had an inkling about it even before I left last time because I had a meeting with Kate Oates who pitched the idea to me; obviously I was hugely excited about it and said yes there and then.

[Quiz: How well do you know the Platt family?]

Kate needed to go away and speak to the storyline and writing team and come up with ideas as at that stage it was just a very small grain of an idea in her head and she had to sound other people out to make sure they were on board. Fortunately they were so here we are.

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At the time you didn’t know when it would happen?

I had no idea it would be eight months away. I knew that they had already storylined three months on from the attack on Andy but fortunately everything all fell into place and when they finally called I was available for the filming dates.

How did you feel to hear that Andy was not going to be dead?

When I first read the scripts where Phelan attacked Andy I thought he was dead, I think we all did. Luckily that meeting with Kate came not too far after so I knew he may still be alive but nothing had been finalised so I was in some weird sort of limbo.

When some months later was finally told the storyline I thought it was amazing and I couldn’t recall a time it had been done before in a soap. I also felt it was not beyond the realms of possibility because you see cases in the news like this. I felt it was a brilliant original credible story that we would put meat on the bones of.

How important did it become that it had to be kept a secret?

I knew it had to be pretty secret from the off but as Kate evolved the storyline it became more and more apparent that a big reveal would make this story work best from the outset. It’s been fun, difficult, exciting and challenging to keep that secret going.

Have you told anybody what you have been up to?

I have told a few close friends and family an inner circle that I would trust with my life but apart from that no one else really knew, even a lot of people at Corrie didn’t know.

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How did you feel knowing that you weren’t even allowed to come into the building and see all your friends in the green room and canteen?

I felt a bit like a movie star being driven in my own personal car to set every day and come out with sunglasses on and a hood over my head to avoid the paparazzi. I thought it was ultimately hilarious and part of the challenge so I accepted that.

It helped in some ways for the role and mental preparation to be isolated from everyone: at Corrie there is a great green room where everyone relaxes and chats and it adds to the convivial atmosphere that the show creates, but because the storyline is so dark and isolated filming away from the normal set has been helpful.

Even on location at lunchtime I would take myself off without thinking and sit in my dressing room and eat on my own, not because I was being antisocial, you just get into that mindset. I am by no means a method actor but keeping that going all day really helped to get into the role.

How did you research? Did you read any of the stories about people being held captive?

Yes there is the very dark awful stories that you hear, the Fritzel case I was aware of and crimes of that ilk. As an actor you have to have that awareness and that knowledge.

I didn’t look at specific cases as each one is different and Andy’s journey is something I need to think about and create on my own. I spent a lot of time just thinking about the different stages he would have been through during the past eight months from hope to despair to seeing Phelan as an arch enemy to sometimes possibly even seeing him as a friend. If Phelan leaves him alone for a few days without food, the second he comes in with a sandwich he has to be his best friend as Phelan has got something that Andy needs for survival.

How did you find growing the beard?

I knew that was coming so I spent about three months growing my beard and my hair and I grew my nails a bit longer. When I get on set they put an olive oil spray in my hair so it is really lank and greasy and they put dirt all over me and stuff under my finger nails. It sounds like dressing up but that and putting on filthy clothes really helps get you into the mindset of the character.

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What is the set like?

The set is absolutely incredible, it is an inch-for-inch remake of one of the worst basements you have ever seen. It has wet musty damp walls, but it has a sixties kitchen area in one corner that at some point has been ripped out but some of the old wallpaper is still there, and old light switches that don’t work. The attention to detail has been amazing and getting in that room all helps with feeling how Andy would feel.

I have even taken to putting my own chains around my leg - it is something I do as a kind of ritual, it just helps me to go through the motions before every take and as  I lock myself up so it reaffirms where Andy is at and his plight.

Is it quite oppressive working on that set - how do you feel at the end of the day?

Relieved to be in the open air. If we finish filming early to come out and see sunlight you really appreciate it. You don’t take a nice day for granted. If we had been filming in the middle of winter it might have been a different story. It’s not too difficult to shake it off though.

So now we have finally had a glimpse of Andy in the cellar. What sort of state is he in?

I filled in a lot of it myself. I imagined what he would have gone through in those eight months and we join the storyline where he is in a state of almost feeling the end coming and he is just desperate.

Do you feel some sort of Stockholm syndrome has set in, what is his relationship with Phelan?

Stockholm syndrome is something I researched and it is an interesting phenomenon. If you spend that amount of time as someone's prisoner then there is a bond of sorts between Andy and Phelan, and the kind of dependency that Andy has on Phelan might have started to work the other way round.

Phelan has kept him there for all this time - why? What is Phelan gaining from it? He could have killed Andy eight months ago or numerous times since, he has the perfect place to dispose of the body, he knows that no one is really looking for Andy any more: Steph thinks she has been dumped and Luke is annoyed with him so no longer looking for him. So what is Phelan’s relationship with Andy?

Connor McIntyre, who plays Phelan, says that Andy is the only person who truly knows Phelan - could that be it?

Yes, he is the only person who knows every face of Phelan, every side of him. Some people know nice Phelan, some people have been crossed by him but Andy is the only person who knows everything about him.

When the door bolts go and Andy knows Phelan is coming he never knows which face of Phelan he is going to get: is Phelan angry, is he going to use him as a punchbag? Has he had a good day? Will he have brought him treats? Will he want to confide something in him, will he want to sit there and rage, will he want to cry in front of Andy?

It is a very controlling relationship, Andy never knows who will walk through that door as Phelan is so many different people. It is almost like Phelan has got him there as something to rage at, talk at and doesn’t feel he needs to hold anything back from Andy so he has seen many sides of him.

What has it been like trying to keep the secret while filming?

It has been brilliant. We have had a few tricks up our sleeve: I have had a car collect me and take me everywhere hidden in the back, I haven’t been able to walk to work or get the tram to Media City.

When we filmed on location we had a plan where I was driven to one place in my car and switched with a member of the production team who was dressed in the same coat and hat.

The paparazzi took pictures of him while I was put in a Land Rover under coats and driven up a lane to another entrance. All the secrecy and filming the scenes is very different to how I have worked before on Corrie, from the lighting to the way it has been shot.

It has been challenging but in a really good way. I have relished it, playing the same character I did before but a kind of crumpled up and put-back-together version who doesn’t know what is going to happen to him next and has no control over his life.

What has it been like working with Connor?

He is brilliant, he is fantastic on screen, but off-screen too, he is great on set, he always wants to find every grain of truth we can get in a scene, he wants to rehearse them which I enjoy doing as well - he is very generous as an actor. We learn from everyone we work with and I have definitely learned from him.

Why hasn’t Phelan killed Andy?

We just don’t know, he could have killed him during the attack in the heat of the moment but it is different now if someone is still alive. He has never killed in cold blood: he watched Michael die but he didn’t actually do it. He has moral responsibilities, he has real catholic guilt as we saw in the confessional.

Do you fear for Andy now that the net is closing in on Phelan: is Andy in more danger?

I think so and I think what we see now is desperation from Andy. He has seen a shift in Phelan’s behaviour, an air that Phelan is acting more on a knife edge, even more unpredictable and strained which is why he thinks the time has come to try and escape.

Are you looking forward to walking through the front gates and properly catching up with everybody and telling people what you have been doing?

It is going to be great to sit in the green room and have a good old chat with everyone and celebrate keeping the secret.

What reaction do you get off people when you are out and about? Have people said they think Andy might still be alive?

Yes definitely some people. My litmus test is the ladies in my local Co-op who I used to chat to when I was in the show the first time around. They have been asking me what I am up to and some of them say they think Andy might be alive and some say he is definitely dead.

They did give me some advice about getting another acting job though: they said maybe I should think about shaving off the beard and getting a haircut as it probably isn’t helping. At least now I can go and tell them why I looked like that!