Every evening, as the sun was setting over the skyline of Rome, Hugh O’Flaherty would stand on the steps of St Peter’s Basilica, in Vatican City, in full view of armed Nazi soldiers stationed across the piazza. He was taunting them. They were incensed because they knew this Irish Catholic priest was hiding refugees under their noses, and they couldn’t for the life of them work out how.

If O’Flaherty had strayed one inch across the international border between the tiny, neutral city-state of the Vatican and German-occupied Rome surrounding it, the Gestapo would almost certainly have pounced, torturing and killing him.

Now their extraordinary cat-and-mouse story is the subject of a thrilling new novel by Irish author Joseph O’Connor, My Father’s House. Although fictionalised, it sticks closely to the high-stakes story of this Second World War hero from County Kerry who masterminded a vast and intricate network for around 6,500 downed Allied airmen, escaped POWs and Jewish refugees.

The risks he took and the ways he outwitted the Nazis are similar to those of Oskar Schindler, the German industrialist who saved 1,200 Jews in eastern Europe, and whose exploits were made famous in Steven Spielberg’s 1993 film Schindler’s List.

O’Flaherty’s charges were hidden away in 60 or so secret locations dotted across Rome – churches, convents, seminaries, monasteries and sometimes just the ordinary homes of sympathisers. They often had to disguise themselves as nuns, monks, bus drivers and ordinary labourers in order to evade capture.

The priest and his secret organisation of anti-Nazi collaborators provided them with food, clothing, money and even forged identity papers.

“The escape route became a passion for O’Flaherty,” O’Connor says. “Everyone was telling him not to do it – from the Germans, obviously, and the Irish government which was neutral during the war, to the papacy who wanted to protect the Vatican’s neutrality and not give the Germans a pretext to invade.

“But he couldn’t help but do it.”

O’Flaherty’s ability to evade Nazi capture later earned him the nickname “The Scarlet Pimpernel of the Vatican”.

Appointed a papal chamberlain, with the title of Monsignor, the priest worked under Pope Pius XII, and initially toured allied POW camps in Italy as an international observer.

Later, when the Germans occupied Italy, thousands of these prisoners and other refugees fled to the 0.19 square-mile safe haven of the Vatican City, seeking help from the compassionate Irishman.

“The Vatican was a neutral state,” explains O’Connor, the renowned author of the award-winning 2002 novel Star Of The Sea. “The Nazis were not supposed to invade the Vatican. But there was always a threat and very heated fears about the imminence of an invasion.

“One radio station would say, ‘We have it from a very good source they’re going to invade in two weeks’. Another station would say: ‘They’re going to invade tomorrow’.

“If you’ve been to Rome, you’d know how little of an effort that would be for the Germans.

“It literally would have been a case of rolling the tanks a few yards across the piazza into the Vatican.”

O’Flaherty’s nemesis during all this was Herbert Kappler, a leading figure in the Gestapo, and the man in charge of security for Rome. As far as Nazi villains go, he was one of the most evil of all. In March 1944, he oversaw the murder of civilians in the outskirts of Rome, known as the Ardeatine massacre.

Some 335 people, mainly political prisoners and Jews, were transported by lorry to a cave system in the south of the city.

There, they were handcuffed, frogmarched into an underground cave, and forced to kneel before being
shot. So full was the cave that many were pushed onto dead bodies before being murdered themselves.

Kappler was such a monster that, when O’Connor came round to writing his novel, he felt forced to fictionalise the Nazi, changing his name to Paul Hauptmann. “He was a ruthless thug who did terrible things,” he explains. “For some completely personal reason I don’t understand, I didn’t like typing his name. I don’t actually want the sh** b*****d remembered. I didn’t want him in my book. I didn’t want to be thinking about him. I thought: ‘I can deal with it if it’s a fictional character but I don’t want to deal with you’.”

The real-life Kappler laid several traps in his efforts to capture O’Flaherty.

In March 1944, two Gestapo agents attempted to bundle the priest across the Vatican border – a simple white line painted on the ground – and into Rome.

According to one account, burly Vatican security guards gave the Nazis a sound beating for their efforts.

Another time, when cornered by Kappler and his henchmen, O’Flaherty escaped into a coal cellar, stripped out of his priest’s
robes and rubbed coal dust all over his skin so as to trick the Germans into thinking he was a coal deliveryman.

For months, this deadly game of cat-and-mouse continued.

In many ways, O’Connor believes O’Flaherty was probably just as tough as the Nazis pursuing him. “He was a rather old-fashioned movie hero type,” the author says.

“He loved boxing, and he was a ballsy guy. His version of masculinity was very much of its time. He liked tough guys in the movies – cowboys and gangsters.”

But the Irishman was also highly educated.

“He was very scholarly. He spoke seven languages, had three doctorates and loved choral music. I would have loved to meet him.

“Having written the book, I feel like I’ve met him.”

In researching his novel, O’Connor – the brother of pop singer Sinead O’Connor – spent many weeks in Rome, reflected in his brilliant depiction of the sights, sounds and smells of the Italian capital during wartime.

“To watch the handsome women going about, the mocking way they argued with the stallholders,” he writes. “Ardent lovers, hand in hand, glitter-eyed and gesturing… Romans are like people stepped out of a Caravaggio, long-nosed, alluring, courtly. The street singers, the vagabonds, the bawling men arguing…”

As a fictionalised account of O’Flaherty’s story, My Father’s House strays from real historical events, although, as O’Connor insists: “It’s pretty accurate. But it’s not a textbook, and it aspires not to be one.”

In all, O’Flaherty and his brave friends succeed in saving thousands of Allied and Jewish lives. And the Gestapo officer Kappler?

He was eventually captured by the Allies and, having escaped the death penalty, imprisoned for life in Italy.

O’Flaherty visited him in prison and, years later, in the ultimate act of forgiveness, agreed to baptise him into the Catholic church.

In 1977, in a plot twist that almost defies belief, Kappler was smuggled out of prison by his second wife in a large suitcase, and escaped to West Germany.

Sick with cancer, he died six months later.

As for the priest, O’Flaherty was awarded a CBE and the US Medal of Freedom for his humanitarian work. He continued his church work after the war, dying at his sister’s home in County Kerry in 1963. In Killarney, the town he was raised in, a memorial statue commemorates him and his efforts to save so many lives.

• My Father’s House by Joseph O’Connor (Harvill Secker, £20) is out now. For free UK P&P, visit expressbookshop.com or call 020 3176 3832