This is the tale of two IRAs, the Officials and the Provisionals, which split in 1969 over whether to reform or destroy Northern Ireland. The Officials renounced violence and their political wing embarked on a journey on which its most gifted parliamentarians became leaders of the Irish Labour Party. However, the Provisionals prevailed in the early 1970s even as the peaceful civil rights movement emerged successfully to tackle discrimination. They became "the most well-armed and sophisticated paramilitary force in the western world", according to this veteran Ireland correspondent's book.
The supreme irony is that the Provisionals' belief in sickening the UK into abandoning Northern Irish Protestants has substantially or perhaps permanently deferred Irish unity. "A charade of gunsmoke and mirrors" has subsequently covered a retreat from their early revolutionary rhetoric as Sinn Fein plays catch-up with the Officials and the Social Democratic and Labour Party.
This fast-paced and passionate (but occasionally sloppy) polemic is a scathing indictment of republican illusions and brutality, without neglecting loyalist and state actions, in a conflict that claimed thousands of lives and cost billions. Henry McDonald argues that the Provos spent years sending violent messages to "the wrong address" - to the UK Establishment rather than the local Protestants. They were long dismissed as imperialist stooges but are now being "love-bombed" by Sinn Fein, which requires some of them to amass a majority for unification.
Republicans failed to cajole the UK into withdrawing and being a persuader for unification. Instead, London built solid relations with the Irish government and insisted that Irish unity required consent rather than coercion. In the 1990s, republicans gradually dumped the ballot box and Armalite for an unarmed strategy to advance a unitary Ireland through an alliance of UK sympathisers, nationalist Ireland in the 26 counties, and American supporters.
However, these hopes evaporated and Irish unity seems unlikely by 2016 - the centenary of the Easter Rising. Partition is an increasing fact of life in the Republic, where Sinn Fein is more isolated because it is seen as irrelevant to domestic issues. Hostility there has also been fuelled by several high-profile, bitterly contested and so far unresolved murders.
The United States became less sympathetic after the 11 September 2001 attacks, and even before that the IRA's dalliance with Farc narcoterrorists in Colombia infuriated the Bush administration, which rounded on Gerry Adams. The senior US diplomat Richard Haass told him: "If any American, service personnel or civilian, is killed in Colombia by the technology the IRA supplied then you can fuck off. Don't tell me you know nothing about what's going on there, we know everything about it."
When one factors in heavy infiltration of the IRA by British agents and the possibly connected elimination of militaristic elements, it is not surprising that a movement which promised to smash Stormont and never decommission reversed both commitments at the end of "one of the most futile mini-wars of the last century".
Where now? There is much talk of some sort of truth recovery process. However, in my view, Northern Ireland is too small, the events are too fresh and politicians have no interest in coming clean and possibly losing votes. Yet those who died and suffered deserve justice.
McDonald concedes that Sinn Fein ministers are "among the most personally amenable and human in their handling of the press and the public". This counts for something, but new politics and generational change in parties that sustained violence are also needed.
The critical change which came with the Good Friday Agreement is that most political forces are now trying to overcome the legacy of accumulated bitterness within Northern Ireland rather than obsessing about the border, which is what republicans split over in 1969. For example, Sinn Fein, Conservatives and others on the British-Irish Parliamentary Assembly are seeking to transform the sprawling army base at Omagh into an educational village where Catholic and Protestant schools will share facilities.
Increasing integrated education, which covers just 6 per cent of pupils, will be important in undermining the sectarianism of a deeply segregated society. A "peace wall" was recently erected in one integrated school's playground but a wider benign apartheid allows Protestants and Catholics still to live separate lives. The creation of a smart civil society and a sound economy, which spends less on duplicating expenditure along sectarian lines, would bolster a stable Northern Ireland with full equality and substantial north-south co-operation, or even Irish unity.
McDonald's many insights add to the burgeoning literature on the rise and fall of the Troubles and the future of Northern Ireland. Peace is better anchored there but still bitter and fragile. This book analyses key aspects of the long journey, but there is much further to travel.
Gary Kent has written about Irish affairs since the 1980s