In Brighton in early April of 1974, ABBA won Eurovision for Sweden. It would be the first of the country’s seven wins to date. Portugal’s entry, “E depois do adeus,” sung by Paulo de Carvalho, tied for last place. Despite its poor performance, the song was on heavy rotation on Portuguese radio in the weeks after the contest. Its innocuous nature and ready availability on tape in Lisbon’s EAL radio station led de Carvalho’s not-quite hit to be selected by a group of young military officers as the signal that their planned coup was underway.

De Carvallho would enter the history books crooning on a far bigger stage than Eurovision. Twenty-four hours later, on April 25, Portugal would be free from forty-eight years of dictatorship. Most people are probably more familiar with “Waterloo” than “E depois do adeus,” but as Alex Fernandes tells us in his new history of the 1974 coup, “ABBA never started a revolution.”

Released in time to mark the fiftieth anniversary of the overthrow of the dictatorship, The Carnation Revolution reads more like a thriller than a history book, taking the reader through the conspiracy of young captains who brought a democratic Portugal into existence.

In 1974, Marcelo Caetano led Portugal, having replaced António Salazar as prime minister six years earlier. Despite some hopes of a “Marceline Spring,” the change of personnel at the top did not loosen the grip of the Estado Novo, or “New State,” the intensely repressive regime that had been in place since 1926. Under the regime only a small fraction of the population — the wealthy, conservative elite — had the franchise, rendering elections a farce. An extensive secret police force, the PIDE, kept an ever-watchful eye on dissidents. Opponents of the regime — many communists, but by no means all — often found themselves in Lisbon’s notorious Aljube prison, subject to sleep deprivation, beatings, and other forms of torture, mostly lifted from the CIA playbook.

By the 1950s, despite dense networks of government informers, threats of imprisonment, and a political system designed to make removing Salazar seem “as absurd as removing one’s own head,” discontent was growing within the New State. In 1958, General Humberto Delgado’s bid for the presidency drew popular support on the streets before being crushed by vote rigging at the ballot box. Delgado went into exile in Brazil, and the failure of his aboveboard bid to challenge the dictatorship spurred a series of more drastic challenges to the regime in the 1960s, most notable among them the hijacking of the cruise liner Santa Maria, complete with almost a thousand passengers and crew, by fighters instructed by regime opponent Henrique Galvão.

Despite the dramatic hijackings and improbable jailbreaks of the 1960s and early 1970s, many of which Fernandes’s book lays out in nail-biting detail, the call that would ultimately topple the regime would come from inside the house: the officer class of the Portuguese army.

Having lost its Indian colony in 1961, throughout the 1960s and ’70s the country was engaged in grinding colonial wars on several fronts in Africa. Portugal attempted to suppress independence movements in Angola, Mozambique, and Guinea-Bissau and hold on to the colonies that were central to the regime’s self-conception. The wars were going badly, and increasing numbers were conscripted: by 1973, Fernandes tells us, “a significant majority of Portugal’s male population of recruitable age [was] fighting overseas.”

Young officers sent to these fronts returned combat experienced, often politically radicalized, and with no faith in the command that had sent them there. The regime’s one-more-push propaganda couldn’t fool those actually fighting the wars, and the relationship between the state and its officers grew increasingly tense. A group of officers, initially mostly young captains, began to meet in late 1973. At first without concrete revolutionary intent, the conspiracy eventually came to the conclusion that, in the words of one officer, “the government will only leave with gunfire, and the only ones capable of making them leave are us.”

Fernandes’s book reads like a screenplay of a ’70s spy caper, or the basis of one — perhaps unsurprising given the author’s background working in theatre. After spending a few slower chapters establishing the context that pushed the members of the Armed Forces Movement (MFA) to contemplate armed revolt, it kicks into gear to describe how, exactly, the officers managed to meet, plan, and execute the overthrow of the dictatorship.

With the limited communications technology of the early 1970s and a need for secrecy, descriptions of how dissidents plotted against the regime — inane letters with meaningfully underlined signatures, cryptic messages in the football pages of the newspaper — have a quaint analog feel.

The plan of operations for the day of the coup was scrawled out by hand over twenty-six pages. Whole sections of the book feel like they’re taking place in a smoke-filled car at night, and no opportunity to sweat the tension is missed: plotters sleep through alarms and unreliable elements abscond to strip clubs at key moments. Everyone is stressed, one officer so much so that he spends the entirety of a planning meeting lying face down on the carpet. Even the musical cue that set events in motion didn’t go off without a hitch: the MFA had arranged with the radio presenter that the song would play at 22:55, but at 22:48, the station encountered technical difficulties, and the plotters, crowded around radios around the city, endured an agonizing three minutes of static. The station came back online and before hitting play on the song, the presenter spoke the agreed line: “it’s five to eleven . . .”

The group’s scramble for ammunitions in advance of April 24 was only somewhat successful: on the day of the operation, many soldiers went out with empty guns. Nevertheless, when they descended on the streets of Lisbon they were met with support from the public, and from communist militias who scraped with PIDE agents on the rooftops while revolutionary soldiers faced off against regime loyal army sections down below.

Officers on both sides know one another, and many of the government’s men shared the plotters’ unhappiness with the state of affairs. Although many regime loyalists were not willing to join the coup, they were also unwilling to put it down. By the end of the day, Caetano had surrendered himself to the ambiguous figure of General António de Spínola, soon to become the first post-dictatorship president, without any military clashes. The four casualties of the revolution — three civilians and an off-duty solider — were killed at the headquarters of PIDE, where agents fired into the crowd of protestors on the street, while inside their colleagues frantically shredded documents.

The Carnation Revolution is a clear and pacey account of the construction and execution of a coup. What it offers less of is political analysis. Of the officers’ program (“This is a coup to topple the regime, have free elections, end the colonial war, free political prisoners, and put an end to PIDE and censorship,” one soldier on the street tells a journalist) we get a fairly minimal treatment; similarly so the views of other dissidents, and the differing analyses and motivations of those who tried and succeeded to bring down the New State.

The book’s final chapters turn to what happened in the first juddering, chaotic eighteen months after the regime fell, as the MFA worked out its relationship to the nascent democracy and to Spinola, who pushed against the decolonization agenda of the left-wing younger officers that had led the overthrow. In these closing, more politically complicated sections, the book loses some of its lucidity and atmosphere. This seems like a petty criticism, however, for a book that manages to tell the story of the revolution with just as much vivid propulsion, tension, and intrigue as it deserves.

Portugal is getting ready to mark fifty years since the revolution, and Fernandes’s book ends with a discussion of recent attempts to defang and reframe the Carnation Revolution, including branding it an “evolution” — an attempt, the author says, to “sanitize and compartmentalize” the radical events of 1974. Fernandes also issues a warning about the rise of the far right as the events of 1974 and the reality of the dictatorship fade from younger people’s living memory. This is a warning that has already proved prescient: at the general election in early March, the reactionary Chega party surged to third place.