For some reason, best known to the powers that be, grave, secret service blokes have come up from their hideouts to issue sombre notices about the threat of terrorism in the UK.
Andrew Parker, the MI5 boss, believes our nation is more imperilled than ever before by evil Islamicists who are either bubbling up explosive materials in their kitchens or sneaking back in from ravaged Muslim countries with murderous plans.
Parker claims the danger is "at the highest tempo", what with "plots, scheming and crude stabbings, lengthy planning and ...spontaneous attacks". He sounds like a Crusader.
The excellent and erudite columnist, Sir Simon Jenkins, roundly rubbishes Parker's claims and suspects this is a naked resource and status bid by spooks. I am less sanguine than this knight of the realm.
I know, through my work as a journalist, that many British Muslims have turned venomously anti-West. Some have grievances I understand and share; the calamitous Western military action in Afghanistan, Iraq and Libya; the unaccountable, oppressive policies of Israel; the cruel demonisation of refugees from Syria and other devastated lands; racism.
But too many others just want to cause maximum hurt and feel, briefly, like cowboys of the eastern world. There are those about whom we know little – the mentally unstable, inchoate nihilists and suicidal no-hopers. It is unwise to breezily dismiss the dangers they pose to us and themselves.
Blameless British Muslims fear these possibilities even more than non-Muslims. When terrorist acts are carried out by proficient operatives or by demented lone killers, the rest of us feel collectively blamed and abhorred.
In some ways I do understand these instinctive reactions. If my child had been blown up by a Muslim terrorist at a pop concert in Manchester, I might never find tolerance in my heart again for Muslims or their faith.
Emotion is a potent force. It is remarkable that good citizens of Manchester and London did everything to keep going, determined to remain undivided as the dreadful tragedies unfolded. Racists, however, seized these moments, and did their worst.
Hate crimes against Muslims have increased fivefold since the Westminster and London Bridge attacks. That, in turn, will be raising more Muslim fury and so it will go on for a very long time. Now this deadly brew is likely to become even more bitter and toxic.
Hundreds of British Muslims – mostly men, but some women too and many children – have either returned to this country from Syria and Iraq or are on their way, as Isis faces military defeat and loss of territories. Parker's doom-laden views partly come from this new, unprecedented challenge.
So what to do with the returnees? That is the question. Noisy right wingers want internment; nothing else will pacify them. Katie Hopkins probably would be happy if the government could come up with a 'final solution'.
Thankfully, this country still has some sense and sensibility. On Radio4's Today programme, two experts, Max Hill, the independent reviewer of terrorist legislation and Richard Barrett, the former MI6 global anti-terrorism director talked rationally about the problem without bombast and patriotic patois ('great British values', loyalty tests, etc).
Thy reminded listeners that returnees were not all alike or equally dangerous. Different reasons took them out there and there will be differences between them as they try to resettle.
Skilled Intelligence professionals should be able to separate the real hard nuts from the easily manipulated, the truth tellers from the practised lairs, those likely to carry out violent acts from those who are passive believers an Islamic global victory, incurable fantasists from those who are 'awoke' and regret what they did, the mad from the really bad.
There are also the totally innocent men and women who went to these countries to help civilians. A young medical student I vaguely knew, took off to go help Assad's victims. He has never been seen again. His distraught parents don't make official enquiries. He might be dead, but what if he joined Isis? They fear ostracisation and no longer go to mosque.
The final and most difficult decision is what to do about the children, many of whom have been thoroughly, mercilessly radicalised. Those who knowingly became Isis guerrillas must face due process. But various others may require state compassion and resources to find themselves again and fit in.
Progressive Muslims, empathetic politicians, police forces, educators and international aid charities all have a part to play in this process. The outcomes can't be predicted – some radicalised Muslims will never reintegrate – but the rest deserve a chance, for their sake as well as the sake of the country.
Even at these taxing times, the urge only to punish has to be curbed. If it isn't, a liberal democracy will become an elected autocracy. And then no one is safe.