It’s often said that Italy has managed to get away with its fascist past. There’s no great communal guilt or shame; the country paid a pittance in terms of war reparations. Of course the crimes of Mussolini’s thugs, horrifying as they often were, seem minor when set against the industrialised genocide of the Third Reich. Mussolini was many things, but his racism always felt half-hearted, his antisemitism merely favour-gaining with Hitler.

There’s something else, though. Italy’s resistance to fascism and totalitarian rule was more widespread and well organised than in any other European country (even, arguably, France). The nobility and heroism of the loose nexus of socialists, Freemasons and academics who stood up to Mussolini provided a narrative upon which the country could found its postwar identity. Foremost among the opposition to fascism, there were two portly, bookish, Jewish brothers who shone brightly, briefly, before their early deaths at the hands of the regime. Their names were Carlo and Nello Rosselli.

Caroline Moorehead’s lucid, readable and superbly titled biography of the brothers opens with the murder by fascists of the socialist politician Giacomo Matteotti in June 1924. This, she argues convincingly, was a turning point, both for Italy – it was the beginning of a dark new chapter of political violence – and for the resistance – it was the event that knitted together the disparate strands of dissent. The murder, in which Matteotti was bundled into a car by the fascist secret police, stabbed repeatedly with a carpenter’s file, and dumped in a ditch, inspired lasting outrage among the Italian left, leaving a mark on the young and impressionable Rosselli brothers in particular.

That the Rossellis aren’t typical action heroes gives the story of their reckless heroism and murder added poignancy

After this bloody opening, Moorehead winds back to the birth of the Rossellis’ mother, Amelia Pincherle, in Venice in 1870. The rationale for this is clear: not only was Pincherle the source of her sons’ erudition and idealism, but the book also relies a great deal on her correspondence with the boys, in her wonderful memoir, Memorie, published in 2001.

A deep and fascinating bond appears to have built between Moorehead and Pincherle, so that it’s almost as if the biography is written through the mother’s eyes. Pincherle was a formidable woman, full of the noble spirit of the Risorgimento. She was also the leading Italian playwright of her age, and this lends the book an unusual literary quality. Moorehead’s narrative laces seamlessly between her own voice and that of Amelia, so that there are numerous observations and passages that hum with life. Take for instance, the description of Amelia’s Venetian childhood in which she “turned the chairs in the salotto upside down and pretended that they were gondolas, rowing across a marble lagoon”. Carlo and Nello were also fine letter-writers and authors – the fact that this was a family that cared about words (Alberto Moravia was the boys’ cousin) gives Moorehead’s book a richness and poise that’s rare in a political biography, more novel-like than journalistic.

Facebook Twitter Pinterest Benito Mussolini in Rome in 1927. Photograph: Universal History Archive/UIG via Getty Images

Like any good biography, A Bold and Dangerous Family is about far more than its subjects, and it’s hard not to feel regular little shivers of horrified contemporary recognition at the rise of the populist demagogue Mussolini. It’s a book about resistance and valour, about Italian life and the uniquely integrated place of the Jewish community within it. Moorehead moves breezily through the history, grounding it in the lives of her protagonists, dropping the reader into key events, so that we feel as an almost personal outrage the lurch from the optimism and inclusiveness of the Risorgimento to the brutality of Mussolini’s rule.

We see Vittorio Orlando, Italy’s prime minister, returning “crushed” from the Treaty of Versailles. We see Mussolini starting off as a socialist, then declaring himself a man of the right, one whose politics would be shaped by “the great, the beautiful, the inexorable violence”. We see the flip-flopping of the opposition to Mussolini (there’s a nice line in the description of the chaotic horse-trading of the pre-fascist era of Italian politics in which Moorehead gives us transformismo – “the hanging on to parliamentary majority through alliances with often incompatible partners” – Theresa May might want to save that one for her next trip to Europe). We see the elections of 1921, in which more than 500 people were killed or wounded. Finally, we see Mussolini assert a terrible and total grip on power through his roving brigades of squadistri. As Carlo put it in a letter to his mother: “An enormous black plague has settled on the body of Italy.”

A picture gradually develops of the boys – Carlo, slightly older, bespectacled and thrusting; Nello, more circumspect and poetic. Both boys were pudgy (when Carlo makes a daring escape from the prison island of Lipari to Tunisia, he’s unable to find clothes that fit him), academic and extraordinarily brave. When the Spanish civil war broke out, Carlo, living in exile in Paris with his family, immediately borrowed a white beret from his wife and went off to fight (with great distinction). Nello met every new trial, trumped-up charge and imprisonment with unquenchable good humour. When we picture the boys in our mind, we always see them smiling.

The fact that the Rossellis aren’t typical action heroes gives the story of their reckless heroism, their insuperable idealism, their tragic double murder, added poignancy. The boys are nerdily immersed in the recondite world of political philosophy (both Benedetto Croce and Antonio Gramsci helped forge their political consciousness). We read that “Carlo returned to London to learn more about guild socialism”; later, Carlo and his English wife Marion Cave go off to a hotel on the lake at Stresa where they spend their time translating letters between Marx and Engels. The image of the brothers, ambushed when helping what they thought was a stranded motorist, set upon by the cagoulards (fascist thugs in thrall to Mussolini), stabbed and shot and then lying dead in each other’s arms, is profoundly touching.

On the news of their death, a group of intellectuals including André Breton and Pablo Picasso signed an open letter saying that if the death of Matteotti had signalled the death of liberty in Italy, that of the Rosselli brothers “signed its death warrant in the whole of Europe”. And yet from the organisations that sprung up around the brothers – the Spanish civil war brigades, the Giustizia e Libertà movement that the boys founded in Parisian exile – came the resistance that would play a crucial role in throwing off the yoke of fascism.

Moorehead’s portrait of the Rosselli brothers is at once a political history of pre-second world war Italy, a beautiful literary portrait of two brave young men, and a gripping tale of intrigue, espionage and escape. There have been a number of fine books about the Rossellis – Stanislao Pugliese’s biography of Carlo is particularly good. None, though, have been this well structured, this readable, this deeply involved in the material of their lives. I finished it impressed, breathless and enormously moved.

• A Bold and Dangerous Family by Caroline Moorehead is published by Chatto & Windus (£20). To order a copy for £15 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99