I’ve written extensively on the Second World War in Europe. My eleven books may be works of fiction but the plots are all based around real events that unfolded during the war. That history and the locations I use are all carefully researched. I scrupulously avoid altering the history or any other facts to fit the plots: it’s an important principle that they have to work around the real events and places and not the other way round.

My novels cover most of the countries in Europe during 1939-1945: the United Kingdom and Germany; the countries which fell under Nazi occupation and the Soviet Union which of course spent the war in different camps and just as importantly, the five neutral countries (including Turkey).

What I always try to bring across in my books is the complexity of the war, both in terms of how countries behaved during it and how their populations responded to events – the human side of the conflict. Within the obvious parameters of the war unquestionably being between the Allies and the Axis countries – between good and evil – I try hard to avoid a simplistic black and white approach, when in reality so much of what occurred in Europe in this period was so much more complex than this.

And this brings me to my main point. In my opinion, the most complex country during the Second World War was France. One of the main themes of my latest novel – Agent in the Shadows – is what I describe as ‘the fraught topic of collaboration with the Nazis in France during the war’. Linked to this is the equally difficult subject of the effectiveness of the French resistance during the war, famously described by General Dwight Eisenhower, as having been worth ‘an extra six divisions’.

And history has in many ways been kind to France since 1945, arguably overplaying the impact of the resistance before 1944 and playing down the extent of collaboration with the Nazis throughout the war.

For a good deal of the war the French resistance operated very much on the margins as well as in the shadows. ‘For a long period of the war’ as I say in my book ‘the Resistance was little more than an annoyance for the German occupiers and limited in its effectiveness.’

Indeed, the Nazi occupation of France began on 10th May 1940 but it would be another 15 months before the first German was killed by the Resistance, when a young résistant called Pierre Georges (better known by his subsequent nom de guerre, Colonel Fabien) shot dead a German naval officer at Barbès-Rochechouart metro station in the Montmartre district of Paris on 21st August 1941.

When Paris was liberated on 25th August 1944 the business of myth-making began on the same the day. General de Gaulle addressed large crowds from the Hôtel de Ville, telling them France had been ‘liberated by her own people, with the help of the armies of France, with the help and support of the whole of France, that is to say of fighting France, that is to say of the true France, the eternal message’.

It was a message which somehow managed to ignore the role played by the British, US and Canadian armies along with Polish and other troops in liberating France. It also failed to mention the Resistance: at that time de Gaulle was desperately worried by what he saw as a communist-dominated organisation which was a threat to his authority.

It also failed to acknowledge what is an interest footnote in the liberation of Paris, one that took many years to be acknowledged and is still little known about.  The city was liberated on 25 August by US Army Fifth Corps and the Second Armored Division of the Free French Army.  However, the night before the 9th Company of the Free French defied orders and entered the city by the Porte d’Italie, thus becoming the first Allied troops to enter the city.

The 9th Company was commanded by Captain Raymond Dronne, but around 150 of the 160 in his men were in fact Spanish Republicans, so much so that they were known as La Nueve.  It is believed that a Spanish officer – Amado Grannell, a veteran of the Spanish Civil War – was the first officer to enter the city.

It’s perhaps not surprising that de Gaulle failed to mention this. As far as he was concerned, Paris – and the whole of France – had been liberated by the French people, rising as one, as they had been throughout the war. It had not been liberated by the resistance, or the Allied armies and certainly not by Spanish Republicans.

This then, was the myth. The myth has also come to include not just the extent of collaboration during the war but also the way it was dealt with after it.

Much of the collaboration could be described as low level, or indirect, but nonetheless vital for a successful occupation of France by the Nazis.  For a good deal of the war much of the French population was content to live their lives as before, not wanting to cause too much trouble. In some areas, the resistance was regarded as trouble makers. Then there was the more direct collaboration, better termed as treason.

After the war this was dealt with by the épuration, which translates as ‘the purification’.  There were two main phases to the épuration. The first phase was the unofficial one, known as the épuration sauvage, where the resistance and other groups administered summary justice to those they saw as collaborators. There is no exact figure as to how many were executed in this phase, which is perhaps an indication of how this period has now been forgotten. Estimates of those killed in this phase vary enormously, from a conservative estimate of around 10,000 to others which put the number executed as being over 100,000.

The épuration légale, the official treatment of collaborators. According to Ian Ousby in Occupation, in the period 1944-1953 160,287 people were tried for collaboration. Only a quarter of them were actually convicted and imprisoned. A further 7,037 were sentenced to death, with that sentence actually carried out for just 1,500 of them.

Three weeks after the liberation of Paris de Gaulle arrived in newly-liberated Lyon and addressed the crowds on Place des Terreaux on 14th September. But this time he could hardly ignore the Resistance, describing the city as ‘…la capitale de la Résistance Française…’ He went on to say: ‘How to tell Lyon all the emotion, all the gratitude I feel in this Gallic capital, which was the capital of the French Resistance and which is today a very large city in our France covered with wounds, shining in its honour and carried away by its hope.’

But there was no mention of a profound betrayal which had taken place just a couple of miles north of where de Gaulle was standing that day. And it’s all the more surprising given his own personal interest in the case. By 1942, the somewhat disorganised and ineffective nature of the resistance along with its internal rivalries had been a matter of deep concern to de Gaulle. He was convinced that properly organised it could play a major role in undermining the German occupation – and be an important force when the Allies landed in France, both of which proved to be true.

In March 1943 de Gaulle sent his emissary Jean Moulin to France with a brief to unify the resistance. It was natural that Moulin should seek to do this in Lyon, which certainly while that part of France came under Vichy had been the capital of the Resistance.

Moulin began to make progress: on 21 June 1943 – operating under the code name ‘Max’ – he organised a meeting of the National Council of the Resistance at a doctor’s surgery in Caluire-et-Cuire in the north of Lyon. The meeting was about to begin when the surgery was raided by the Gestapo, led by the notorious Klaus Barbie, the ‘Butcher of Lyon’.

One of the nine Resistance leaders there somehow managed to escape, though he was later recaptured. The rest were taken to the Gestapo prison in Lyon, Fort Montluc. Barbie soon discovered that ‘Max’ was the man who’d been hunted throughout France. Jean Moulin was subjected to dreadful torture and died as a result of this a fortnight later.

But who had betrayed the meeting? My fictionalised take on this is at the heart of the plot of Agent in the Shadows. There is a general, if reluctant agreement that it was most probably betrayed by one of the attendees: the French resistance had a strict protocol regarding meetings, realising they were the times when they were most exposed: generally, only those invited to a meeting would be aware of it and even then, they would be given the details as late as possible. But if there’s an agreement as to who was the traitor, there’s no consensus as to who it was.

Many people suspected René Hardy, who escaped during the raid although was later captured. He survived the war, after which he was twice put on trial for his complicity in the raid and twice acquitted. Suspicion has also fallen on Raymond Aubrac who was arrested at the surgery and imprisoned but who later escaped from the Gestapo. Aubrac was a leading communist and there was a feeling that the communists resented de Gaulle gaining control of the Resistance – which up to then they’d been the most powerful element.

In many ways it is astonishing that eighty years on, the identity of the traitor is as much a mystery now as it was then. More than once, when researching my novel, I was warned that this was a subject I ought not address. Perhaps this is one of those rare examples of where fiction is an acceptable way of addressing an unresolved controversy.

Alex Gerlis is the bestselling and acclaimed author of the Richard Prince spy thrillers, and his new Wolf Pack series starting with Agent in Berlin and his latest, Agent in the Shadows. You can listen to Alex being interviewed on the Aspects of History podcast.