That mystery individual was one of five who had arrived in the village in the mid 1980s to inform on those involved in the miners' strike, such as Gary Jackson. But unlike the others, that person stayed put, with those around them none the wiser – that is until Gary cottoned on, with Scott Rowley now also searching for the encroacher.
During a conversation between Ian and Kevin about who the informant could be, the latter's attention turned to Ian's wife Helen, who was also a colleague of Sarah Vincent, now dead after being killed by Andy Fisher.
Ian informed Kevin that Helen's mum had worked for the National Coal Board, which was responsible for the closure of multiple collieries it deemed inefficient, and the subsequent lay-offs. Ian McGregor, who was head of the NCB, had been appointed by the then Prime Minister Margaret Thatcher.
But that's not all we learned about Helen. When Kevin entered her name into the police database, it emerged that she has a file of her own, and those documents are restricted.
Helen was alerted to Kevin's digging and she contacted him. It's during that conversation that she revealed Helen is not her real name, with the pair then agreeing to meet in person.
Speaking to RadioTimes.com, Sherwood creator James Graham said: "The reason why I hope the drama seems to push away from the true crime genre is I got more excited about exploring the consequences and the aftermath of a trauma like this on people in the community.
"When you place people under pressure, more secrets and more hidden elements seem to spiral outwards into the open, even though they've got technically very little to do with the killings that provoked them. And we all carry around secrets and lies and things from our past that we want to keep hidden.
"There's something about the immense pressure that the village is put under, through surveillance with helicopters and police, that creates a pressure cooker when all of this starts coming to the head.
"In the relationship with David Morrissey's character Ian and his wife Helen, because of David's backstory, because of the trauma he went through and being separated from his family during the miners' strike, making the decision to be a police officer instead of [following] his family's wishes, David's character really goes through the mill; he gets put under intense emotional pressure, which I think is unusual for police officers playing a procedural. It's not always personal to them.
"In episode 4, he discovers, through sheer chance of investigating the 'spycop', that his wife has a police record that he didn't know about, and that is under lock and key. And it's going to contain a secret that will illuminate some parts of this story."
It's not clear how much Ian knows about his wife and her past, or her about his history, for that matter. While their relationship appears to be both happy and stable, that might only be the case because certain truths have remained concealed.
With the investigation ramping up, will Ian and Helen's marriage be able to withstand what's ahead?
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