The 77-year-old secrets of a clandestine Government spy post on the outskirts of east Belfast have been unlocked by an amateur historian who spent a decade trying to find out what went on behind the impenetrable fences of the complex in the Castlereagh Hills.
And now George Busby has published a fascinating book called the Spies at Gilnahirk, which lifts the lid on the vital role that the wireless station, situated amid the lush green fields of a townland called Ballyhanwood, played in the crucial decrypting of coded German radio communications during the Second World War.
George mightn't be a John Le Carre, or a Len Deighton, but piecing together his true-life spy thriller took a combination of the steely determination of a hard-nosed detective and a thick skin.
For the 66-year-old sleuth encountered massive obstacles during his relentless digging for information about the post, which he was to establish was part of an intelligence network linked to Bletchley Park, where code-breakers worked tirelessly to make sense of the messages the Germans were sending out on radio, which has been compared to the internet of its day.
George, a former RAF man and British Telecom employee, was such a dogged researcher that, six years ago, when he gave a talk at Bletchley Park, he was introduced to former employees at a reunion there as "the tenacious ferret". George grew up in the very shadow of the radio station, yet like all his neighbours he didn't have a clue about what they did there.
Not that he was terribly inquisitive as a child. "We learned very quickly that any questions you put to people who worked there were met with no answers," says George, who used to help out a local milkman and had to leave the dairy deliveries at the front gate of the post - they were allowed no further.
However, George's curiosity about the wireless station was triggered a decade ago after a young student sought out his expertise as a historian for a Second World War project, and asked what he knew about the listening post. Which at that time was nothing.
But George was intrigued and resolved to seek out the missing pieces in the Gilnahirk jigsaw. He didn't know what he was letting himself in for and it didn't take long before he realised that establishing the truth wasn't going to be easy.
Many of the former workers had died and some of the ones he did track down were bound by the Official Secrets Act.
So, at first at least, the radio silence was deafening and George was warned by intelligence experts that he was on a mission impossible.
They said he had no hope of eliciting any information because the British had destroyed huge amounts of classified documentation.
But George, who was also a genealogist, didn't give up and he clocked up hundreds of miles in his quest for responses to his questions from the families of the former staff members.
But, like their ancestors, many of the relatives were in the dark about the extent of the Gilnahirk operation, where the right hand had been unaware of what the left hand had been doing.
Indeed, one man didn't grasp what his job at Gilnahirk had actually amounted to until he was interviewed by George, who says: "He thought he was just a tele-printer operator, but I was able to tell him that he was contributing to Bletchley Park, though he took some convincing.
"Ten thousand people were working at Bletchley Park. And unless you were actually at the top of the pyramid, you didn't know the end result of your work."
Gilnahirk may have been near the bottom of the pyramid, but the work that it and the other out-stations around the UK did as they collected what was called raw signals intelligence was vital to the war effort.
George says:"The way it was put to me was that without places like Gilnahirk, Bletchley Park would have been like a car without fuel, going nowhere."
Churchill called the spying operation the goose that laid the golden eggs.
But George discovered that the top secret Ulster war against the Germans across the airwaves wasn't waged only at Gilnahirk.
For scores of unsung heroes joined the Second World War battle in their own homes on their amateur radio sets.
They were called voluntary interceptors and the information they gleaned on their scans was passed on to Gilnahirk who sent it to the headquarters of the Radio Security Service in England.
And if they deemed the intelligence useful they forwarded it to Bletchley Park, where code-breakers tried to decrypt it.
The most famous of the code-breakers was Alan Turing, whose story was told in the movie The Imitation Game. One of his colleagues was John Herivel, who was born in Belfast.
Such was the cloak-and-dagger nature of the work that the amateur radio enthusiasts in Belfast couldn't tell their families about the detail of their activities, and some of them took their secrets to their graves.
The amateurs, who have all now passed away, were expected to man their sets for two hours in any 24-hour period, working on a catch-all basis.
But as the Germans' transmission patterns became more predictable, the volunteers were able to target the broadcasts more easily on what were called special watches.
Incredibly, the amateurs dropped their log sheets in brown envelopes into standard letter boxes on the street, but the address - PO Box 25, Barnet - alerted staff in the main Post Office sorting office, who directed them to Gilnahirk.
James Bond it was not, but the amateur radio enthusiasts regularly unearthed priceless nuggets among the Germans' messages, which were usually in the form of a jumble of letters.
Some of them, including one from a resident of Annadale Avenue in Belfast, have been included in the book by George, who left few stones unturned regarding the innocuous-looking wireless station that had been developed by the GPO in the late-1930s with the erection of a series of huts and telegraph poles, together with an underground facility.
The rumour mill went into overdrive after the wireless station's opening in November 1939, but what the locals didn't realise was that, as the war progressed, Gilnahirk became increasingly important in the Allies' strategies.
Military guards were deployed in greater numbers at the station, to the point where it's been said it was one of the most secure places in Northern Ireland.
Gilnahirk was also to play a vital role in the planning of the D-Day landings by the British, but after the war it closed down in 1946.
However, just a year later, it reopened and, in 1953, a new series of red-brick buildings went up and the post was re-branded as Composite Signals Organisation Station Gilnahirk, which was soon on the frontline of another struggle as the Cold War worsened and GCHQ focused its spying on Russia and the KGB.
Around 100 people were employed at Gilnahirk, but the station, with its 29 100ft steel towers capturing every imaginable signal from the aether, was still shrouded in secrecy.
And even the Belfast Telegraph found out that, while officials were using the post to gather intelligence, they were giving out precious little information about it.
In 1951, after spotting that the Ministry of Finance had tendered for the construction of the new radio station, a reporter bombarded the authorities with requests for more information.
But the buck was well and truly passed and the Telegraph ran a story under the headline "New radio station sets Northern Ireland riddle".
The unnamed reporter wrote that no one in the RAF, the police or the government had been prepared to tell him anything about what they were up to.
Many years later, George Busby met with more success, though he acknowledges that his book may only be the tip of the iceberg.
The wireless station was closed in June 1978 and the Inland Revenue was among its later tenants, before the buildings were eventually razed to the ground.
In 2009, however, the site was bought by developers, and architects borrowed the design of the old place for a new one - a complex of 14 luxury flats called Gilly Court Manor, which took 'Gilly' from the teleprinter address of the wireless station.
Also in 2009, the Government announced it was awarding a badge and certificate to all the people who had served at Bletchley Park and its out-stations during the Second World War. The only condition was that only people who were still living would be honoured.
However, with only two veterans still alive in Northern Ireland at the time, George Busby wrote to then Prime Minister, David Cameron, urging him to recognise the efforts of all the people who had been involved in the intelligence-gathering operation here.
A gold badge and certificate signed by Mr Cameron were sent to the Somme Heritage Museum near Bangor for safekeeping on behalf of the unknown number of Northern Ireland's voluntary interceptors.
It was also agreed that the names of the people involved in the intelligence operation here would be entered into a veterans' register.
Five years ago, George travelled to England for the unveiling by the Queen of a Caithness stone memorial in the grounds of Bletchley Park to honour all 25 of the out-stations in the eavesdropping network.
The name Gilnahirk was carved onto the memorial, which has the inscription, "We Also Served".
As a result of what he learnt at the unveiling ceremony, George was able to make contact with a man who had worked at Gilnahirk. It turned out to be fortuitous.
Ray Wright was living in New Zealand and he sent George photographs of the station he didn't know existed.
"It was quite remarkable to receive them from the other side of the world," says George.
The Spies at Gilnahirk is published by Ballyhay Books. It's available from bookshops and from Hillmount Nursery (www.hillmount.co.uk)