Every cinema in the centre of Belfast was screening Mission Impossible: Rogue Nation while outside in the real world, the PSNI were facing what amounted to their own mission impossible - trying to police a rogue nationalist march and keeping angry loyalists opposed to it in check.
Until late in the day, when there were clashes after the march was stopped on the Oldpark Road, police had succeeded in keeping the lid on a tension-filled scenario, with one of the biggest security operations in Belfast for years, which it's estimated cost a six-figure sum.
Businesses in the city centre were also counting the cost of lost trade during the massive lockdown.
The flagship CastleCourt shopping centre was forced to close for a time as the police turned Royal Avenue into what they called a sterile zone, with access almost impossible for anyone but shop staff. And loyalists.
Three unionist protests were closely shepherded in the area to ensure that they weren't bigger than the limit of 450 demonstrators laid down by the Parades Commission.
As confirmation came that the police were also going to enforce a commission ruling and stop the internment parade before it got to the city centre, the fury among the anti Anti-Internment League protesters, including the DUP's councillor Ruth Patterson, was effectively doused and they went home.
The police had moved in early on Sunday to put the city centre in a complete strangehold, with upwards of 50 Land Rovers and metal screens blocking every imaginable entry point to Royal Avenue.
Police had briefed businessmen about their plans three days earlier and though they couldn't tell them to shut up shop, many of them did stay closed.
However, they put employees on standby to reopen their doors the minute the police told them it was safe to do so.
A short distance away in Donegall Place, it was supposed to be more like business as usual at 1pm, but the normal throngs of Sunday shoppers had been conspicuous by their absence and there was an eerie foreboding that the city could witness a repeat of vicious clashes during the same march in the same area just two years ago, when 56 police officers were hurt.
Dozens of foreign visitors, including a large group of teenage Spanish students, looked bemused as they wandered along Donegall Place, but they made the most of the unexpected photo opportunities presented by police Land Rovers and dozens of PSNI officers strung right across Belfast's busiest shopping area.
The city hadn't seen anything like it since the protests against the G8 summit coming to Fermanagh in June 2013, when thousands of police officers from here and from Britain threw up a ring of steel.
Back then, it appeared that security chiefs had misjudged the numbers of people who would demonstrate against the world leaders and the scale of the police moves was ridiculed as being over the top.
Yesterday, the PSNI said that their "substantial" operation underlined their determination to enforce the Parades Commission rulings and ensure people were kept safe.
Even though it quickly became obvious that the police weren't going to let the internment parade into the city centre, it wasn't quite so certain where it would be stopped, and rumours about the PSNI plans circulated quicker than the traffic in the few roads that weren't sealed off.
At the bottom of the Shankill Road, dozens of loyalists who hadn't made it to the city centre protests vowed to stop the republicans.
The police had other ideas. In Cliftonpark Avenue, two water cannon arrived, ready for action, ready for anything, according to one officer.
On the loyalist lower Oldpark Road, DUP Assemblymen Nelson McCausland and William Humphrey and their party colleague Alderman Brian Kingston from Belfast City Council kept a watching brief and said they expected police to halt the internment march.
On Ardoyne Avenue, hundreds of republicans were in defiant mood as they set off on the parade, an hour after the time the Parades Commission had said it should have left the city centre on its outward journey.
One of the organisers, Alex McCrory, had told protesters to behave in a dignified manner and said anyone who wanted to cause trouble should stay away.
He said the purpose of the march was to oppose the "continued use of internment by remand".
Shortly afterwards, as marchers and their bands emerged on to the Oldpark Road, they could see their way was blocked at Rosapenna Street by eight Land Rovers and several rows of policemen, some of them in riot gear.
On one of the police vehicles, a massive sign warned the republicans that their parade was illegal.
It added: "The parade cannot be allowed to proceed past this point and anyone attempting to do so is committing an offence."
Moments after the head of the parade reached the police lines, a young man waving a tricolour clambered on top of one of the PSNI vehicles, but he was dragged down by other republicans.
One observer said: "It looks like a re-run of the Orange Order marches on the Woodvale Road - only the participants and their politics are very different."
After several speeches, organisers urged their supporters to disperse peacefully and "not to wreck their own communities".
Although most of the demonstrators complied, police didn't drop their guard, with one officer saying they believed that youths gathering in the Rosapenna Street area were hell-bent on trouble.
Not long afterwards, the PSNI fears were realised, as gangs threw at least six petrol bombs and countless bricks and bottles at the police, who responded with the water cannon which had been driven up the Oldpark Road.
One man who lives in the Oldpark area said that troublemakers had been talking up their plans to attack the police for days. He added: "Many of them have been joined by outsiders from Scotland and down south, who are only here to create mayhem."
Further down the Oldpark Road, police had to rescue a nationalist youth who had walked from the Crumlin Road direction into a crowd of loyalists watching the PSNI operation and who gave chase to the young man.
As for the blockade on the marchers, William Humphrey welcomed the police "applying the law to halt this parade of shame", which he said should now be reviewed by the PSNI and the Parades Commission.
"This manufactured policy of opposition to internment, which was phased out 40 years ago, is a nonsense and should not be allowed to go ahead in future," he said.
Back in the city centre, all but a few signs of the police operation had disappeared by 4pm.
A pub which had pulled down its shutters was back in full swing. A Christening celebration which had been in doubt at the height of the lockdown was going strong and the bar owner said: "We've been flat out. It's typical of Belfast people. They don't like anything interfering with their pints and their parties."