For many people, perhaps even some of those responsible, the rioting and looting in London and other cities this week seemed to come out of nowhere.
For now the situation seems to have calmed. But most commentators are unsure about exactly why. Some combination of the large numbers of arrests, a sense of shame on the part of rioters (one man has already turned himself in after seeing his picture in a newspaper) and bad weather are often mooted, but no wider solution to the underlying problems has been identified, let alone implemented.
It is hardly surprising then that even after the disturbances appear to have quelled many people are half-expecting trouble to break out again on the streets.
So how likely is it that there will be more trouble this weekend?
Police aren't taking any chances. Arrests on suspected rioters are continuing apace, as are hearings by magistrates around the country for those who have been charged. More than 1,500 people have been arrested and more than 600 charged.
At least one council has started to try and evicted convicted rioters, with Wandsworth saying it will seek to remove the father of a man charged with offences related to looting from one of its properties.
Authorities have also flagged several potential flashpoints that could spark rioting. The planned season-opening Premier League match between Tottenham Hotspur and Everton at White Hart Lane has been cancelled while other matches, including the home match at Queens Park Rangers, are on the watch list.
Home Secretary Theresa May has banned a planned march by the English Defence League in Telford "to ensure communities and property are protected" and police say that any one of these events and others, including a planned vigil for Mark Duggan, the man allegedly shot by police in Tottenham last week, on the Broadwater Farm estate on Thursday evening, could create problems.
For just as last week's peaceful protests turned into a catalyst for violent riots, police say, any one of many unconnected events has the potential to combust a tense atmosphere into further disturbances.
"We saw initially on Saturday when there was a peaceful vigil outside Tottenham station for the same purpose that rioting developed from that, so that will need to be policed very sensitively," said John Tully, who is vice-chairman of the Metropolitan Police Federation. "Given the context of how things are in London at the moment there would be potential for anything that started there to spread."
Tully said that perhaps an even greater danger is the fact that the demands placed on officers working long hours, many having already sustained injuries, are starting to take their toll.
"Some people are doing 23 or 24 hour stints, then having four hours off and then coming back on. Not everyone is trained to do that sort of thing," Tully said. "About 150 officers have been injured so far. Of those there are a number of broken bones, which fortunately was the most serious type of injury. And people are just turning back up to work if they have bruises and cuts and strains."
Tired officers under pressure opens up the potential for mistakes to be made, Tully adds.
"It opens up the possibility for irrational behaviour to start taking hold, because that's what fatigue does to people," he warned. "Then we enter the scenarios of G20 and people getting injured, and people dying, and police officers being prosecuted, and that's the last thing we want."
For now at least police say they have the resources needed to cope, but in the long term there may be bigger problems ahead.
"We have now got the contingency to deal with problems if they do happen again because, to use the prime minister's word, we can 'surge' police into the area. I don't particularly like that phrase, but we can," Tully said. "But if you look at the other side of the coin where the police are fighting the battle on cuts to police budgets, pay and conditions, that might not always be the case."
Timothy Brain, the former chief constable of Gloucester police and one of the country's more senior police figures, said that the key issue might not be how resilient the police can in the short term but how the force can get back to normality - and what it loses in the process.
"I think in fairness the resilience of the moment is quite considerable. If you cast your mind back to the 1980s when we faced similarly long periods of tension, the riots in 1981 and particularly in 1985 when we had for many weeks on end the expectation of riots and three major riots in Houndsworth, Brixton and Tottenham, a much smaller police service had the resilience to see that through."
"But what I think is the danger is that normal policing begins to suffer, in particular the community policing we've been able to expand in the 2000s. That's the area I fear is under most pressure if the cuts go through."
"It is one thing to maintain these levels in an emergency but we have to get back to normal as soon as possible," he said. "And if numbers have been cut that's going to be a lot more difficult in the future."
Insurance groups estimate that damages from the riots could exceed £100 million. We chart the devastation with these before and after pictures.