Fortitude creator Simon Donald answers some burning questions about the chilling drama

Did Henry (Michael Gambon) know that Dan (Richard Dormer) had killed Billy Pettigrew?

"By the end, yes. By the end, the things he suspected and the things he knew of Dan added up for Henry... by the end Henry basically knew what Dan had done.

"He had never looked at what he saw through the camera. I think right up until he met Morton on the glacier, he didn’t want to face the ghastly truth of what he knew in his heart, and had also seen through his camera lens – that Dan was completely complicit in the savage execution of Pettigrew.

"I always think that it’s related to both the suggestion, the belief that Henry has, that he might be Dan’s father. And also the burden that Henry has carried through his life about his own obsessive love for Carol, who was Dan’s mother, who Henry feels he abandoned. And he’s lived with that in the same way that he understands that Dan has lived and wrestled with his feelings for Elena.

"So it’s a complex understanding that Henry arrives at, which is that Dan is probably guilty but probably also the victim of the same kind of impossible love that he’s lived with all his life – and that he's also possibly his son. He doesn’t know for sure if Dan is his son but I think he strongly suspects he is… He extrapolates what he would do into what he thinks Dan has done, so what Dan does is partly what Henry feels that he himself is capable of."

How did Henry take the photo of Pettigrew's arm without being immediately aware of what Dan had done?

"In the opening sequence when you see Henry walking along the beach and then hearing a scream, there’s a sequence of significant jump cuts. It goes from him hearing something, to looking through his camera, to focusing through the camera, to running, to getting the rifle onto his shoulder, to looking through the telescopic lens on the rifle, at which point he sees Pettigrew and the bear. Prior to that, when he looks through his camera lens, he sees something dangling from the pylon but he doesn’t know what it is and he’s taking a photograph of something but he doesn’t know what that is and he doesn’t develop that photograph."

Why didn't wasps emerge from the first infected person, Frank and Jules's young son Liam, despite the fact that he's still clearly unwell?

"The whole parasite wasp chain of infection involves two hosts. The only thing the wasp does is inject tiny, tiny eggs into the bloodstream of the victim which congregate around the salivary glands and then develop into larvae. And while they’re developing, and the salivary glands are swelling up, filling with mucus that the tiny eggs are in, they’re starting to have an effect on the central nervous system of this primary host which forces them to pass the eggs on, into the cavity of a secondary host.

"They create a cavity by attacking them and hacking them open. So Liam did that, he expunged the larvae into Stoddart and once he’s done that he is free of the burden of having the larvae in him – but pretty fucked up, as a result."

Are the wasps real? Could what happened in Fortitude happen in real life?

"They are called ichneumon wasps. There are around 12,000 species of them. The behaviour of the alien in the film Alien is modelled on the natural history of the ichneumon wasp. It lays it’s larvae inside a live host and the larvae hatch and feed on the inside of the host until they emerge from it. So that’s the stage that we’re at [in Fortitude].

"When I was doing the research, speaking to a parasitologist at the Natural History Museum – and this for me became a really important idea – she said that the really interesting thing about parasites is when they parasitise a host that they haven’t evolved to co-exist with. That is when you get chaos – that’s when things go horribly awry.

"Because most parasites co-exist with their hosts in a finely-balanced arms race. You see it when children get dog worms – it can cause all sorts of psychological disturbances, blindness and so on – so what we did was we took a real parasitic wasp and we brought it into a human population where it had never been before... This is a wasp that existed pre the last Ice Age in that region and had never before been present in a human population. So we get a parasite and a host that have never had any contact before and out of that we get a horrible, grotesque, distorted version of the natural process."

At the end of first series, have they managed to contain and destroy the infection?

"Yes. We see the burning of the mammoth, the burning of Ronny’s house. There’s only one source for it; there’s only one place where the viable wasps have survived and that is inside the frozen mammoth that is thawing, so there aren’t any more coming at us. It’s a really flukish set of circumstances that allowed that to happen so we don’t need to go and search the surrounding area and the town, they’ve burned all the surviving wasps. It’s very, very unlikely there’ll be any more coming out of the perma-frost that have survived 60,000, 70,000 years in very particular circumstances."

But what about the mammoth graveyard Uri finds when he falls down the hole bored by the glacier drill? Something stings him...

"It’s full of mammoths but not all mammoths are full of wasps. And we have to ask ourselves, is he getting out of that hole...?"