Even by the standards of the decade, when the horrors of global terrorism have taken on the grinding familiarity of a recurring nightmare, the attack that left 22 people dead in Manchester on Monday night was an atrocity of singular, unspeakable cruelty.
Armed with a deadly homemade bomb, the killer chose as his target a site where he knew he could inflict large-scale casualties amongst defenceless children and teenagers enjoying a night out. The youngest victim was eight-years-old.
Just as in Paris, Nice, Istanbul, Brussels and countless other cities in recent years, the senseless attack has left families bereft, populations in shock and security services rattled.
Having not suffered a mass killing on this scale in more than a decade, the people of Britain must again confront two grim realities: that the threat of indiscriminate atrocities has become a regular feature of daily life in the world’s major cities, and that free societies cannot entirely eliminate that threat without undermining the very freedoms that define them.
Manchester will deal with this trauma with the same resilience shown by Madrid in 2004 or London in 2005. But with the city still reeling, British police and intelligence services, whose counter-terrorism work has been widely praised, face into a long and difficult investigation.
The concert bombing may not have been as sophisticated as the co-ordinated attacks that struck Paris in November 2015, but it will alarm the authorities that the killer and his accomplices, if any, had the capacity to build, store, deliver and detonate an improvised explosive device in the heart of one of Britain’s largest cities. Was he acting alone? Had he trained overseas? And was he dispatched by a terror network or self-radicalised, inspired from afar?
If Islamic State was responsible as it claims, it will underline a growing fear among intelligence services in the West and the Middle East: the more the group's territory contracts on the battlefield in Syria and Iraq, the more devastatingly it will lash out elsewhere.
In other words, Islamic State's campaign against soft targets in Europe is a sign of weakness, not strength, but defeat for the jihadist network in Syria and Iraq could result in an increased threat to urban public spaces in the West and the Middle East, at least in the short-term.
Although the security challenge is immense, so too is the political one. Leaders must not grant the terrorists victory by blaming Muslims for Monday’s attack.
Nor should they lend weight to the apocalyptic message of the jihadists by framing the current confrontation as a war without end. Instead they must insist all the more strongly on the values – decency, openness, goodness – that set victims and attacker apart in Manchester on Monday night.