BBC One's Vigil has not just been the most-watched new drama of the year, but its also the most-talked about show on the telly too.
But even the team behind the submarine murder mystery have been amazed by the reaction from audiences trying to keep track of the twisty plot full of conspiracy, violence, secrets and espionage.
As anticipation grows among the viewing public ahead of the finale of the blockbuster series starring Suranne Jones, Rose Leslie and Stephen Dillane, Vigil development producer George Aza-Selinger and writer/creator Tom Edge revealed how they brought the world to the brink of nuclear excitement.
Whatever happens in the concluding episode — in terms of deaths, survivors and what is revealed to have been going on — the eagerly awaited finale may not be the last outing for the world they've created.
Edge says: “We had a blast doing it and there are some incredibly talented cast playing characters that we all enjoyed getting to know.
"So I think there are lots of possibilities and if we’re lucky enough to get to explore them further, then that would be terrific. It was a pleasure making this one, and great to get back on board whatever we did next.”
Although they are tight lipped about how the mysteries finally unravel, they’ve been delighted with the online predictions abounding.
Edge said: “We were really thrilled. These shows can be difficult, trying to make something that is intended for a big mainstream audience and it’s very easy to go astray as you shoot for that.
"But that was always our aspiration, something that could go out weekly with its twists and turns, so it’s been great to see the nation clenched at the end of episode five.
“Viewers are so sophisticated that some of the labyrinthine arcane theories about what happened and why, that I’ve been taking a notebook, like ‘that’s good, we should learn from them’.
“One of the nice things is that there are lots of competing theories about how things might end and what might go down, and how situations may or may not resolve, and that’s really fun to watch unfold. I wouldn’t want to spoil anyone’s fun by throwing in my ten pence worth.”
While Aza-Selinger added: “People do the funny thing of saying ‘I’m not gonna ask’ and then begin asking and then retract it. You never want to tell them, and people don’t want to be told anyway, they enjoy being part of the suspense. But yes, people have certainly dangled the question before pulling it away.”
The show began life when Aza-Selinger, head of development with the Scottish arm of World Productions — the company behind Line of Duty and Bodyguard amongst others — had the idea five years ago for a drama about a murder investigation on a sub, coming under the jurisdiction of police detectives due to the nuclear Naval base situated on the River Clyde, not far from Glasgow.
The thriller burst onto screens in late August with a bank holiday bang as Line of Duty star Martin Compston dominated early scenes before becoming the first murder victim.
The team admit that move was a gamble. Edge said: “I was mindful that he is such a great actor and such a beloved actor, as well as someone who a substantial chunk of the population were looking forward to seeing what he does next.
“So there was the worry that if you’re going to take him away really quickly that some people will be disappointed.
“But it wasn’t just a stunt. That character has very limited screen time to begin with but we needed someone who could absolutely capture you in those scenes and allow the echoes of their death to carry through the series.”
Aza-Selinger commented: “He’s got a really important part in the show, he is a large part of the stakes of the show. Apart from everyone’s safety, a large extent of this is all about can we solve this murder and why this happened, so you’ve really got to care about that character.”
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The death of Compston’s crewman Burke may be the incident that draws Suranne Jones’s DCI Silva to the Royal Navy sub in the first place, but it’s also been the spark for a major international plot involving espionage, political skullduggery and murder.
We’ve had US boats tailing Navy allies, spies murdering peace protestors and sparking shady political manoeuvres while a dodgy cook dishes out deep fried nerve gas from the canteen. Affairs abound, while Russian assassins are up to no good in Glasgow and the Navy are still reeling from a mad drugged up party in Florida.
The plot twists have been a plenty – but mainly concurrent with real incidents discovered in the research stage.
Tom Edge commented: “Even though the Navy for the most part and the people who serve in it are incredibly diligent and do a great job under tough conditions, it is still a very human endeavour and the stresses and strains exact a real toll on people.
“Some of the research was indicative of that. There have been drugs scandals, commanders have lost jobs over having affairs on board and there have been whistleblowers, and submariners trying to sell secrets to the Russian embassy. That broke open the human stories and made it intriguing."
Vigil series finale air on BBC One, Sunday, 9pm.
WATCH: Trailer for Vigil