There can be no mitigation, no tolerance of ropey excuses, no quarter given to any dismal defence of the indefensible. This time Chelsea Football Club must do their best to identify the Chelsea fans who sang of their pride at being racist and pushed a black man away from their Paris Métro carriage - and encourage the French authorities to prosecute.
If English football is to point the finger at its counterparts in Russia, or Spain, or Serbia, for their supporters' racial abuse of footballers - if it is to condemn Uefa and Fifa for their inadequate reaction to racism - then this is the moment when it must take its own zero tolerance approach. Chelsea know better than most what a toxic association with racism can do for a club.
At his press conference tomorrow at Cobham, Jose Mourinho will begin by putting aside the football business of life at one of Europe's biggest clubs to condemn those Chelsea supporters' racially charged chanting and put the case that they do not represent the club as a whole.
With 100,000 club members, and another 35,000 Chelsea seasonticket holders, there is a lot of searching to be done to find those responsible, but yesterday sources at the club said names had already been given to them to cross-check with the faces caught in the mobile phone footage on that Paris Métro train at Richelieu-Drouot station.
The club have been shocked by the events in Paris but they are determined that this will not be left unresolved. They will ban from Stamford Bridge those supporters they find responsible and the criminal prosecutions will be left to the French authorities, with the help of the Metropolitan Police.
Put simply, for Chelsea, and the global identity they seek to project of a modern, diverse European superclub in one of the most multicultural cities in the world, the racial abuse by their fans filmed on that Métro station platform is poison.
This is, after all, the club of Didier Drogba, of Michael Essien and Claude Makelele; of William Gallas and Ashley Cole; of Marcel Desailly and Ruud Gullit and Jimmy Floyd Hasselbaink.
This is the club which produced a series of young black players who reached the first team in the 1990s, the likes of Andy Myers, Eddie Newton, Frank Sinclair and Michael Duberry.
This is modern Chelsea, with official supporters' clubs in Bangladesh and Ghana, as well as seven branches in India, four in Pakistan and three in Nigeria. Modern Chelsea is about lucrative summer tours to the United States and the Far East, FFPcompliant accounting profits and social corporate responsibility programmes. The footage from Tuesday night was a jolt back to the bad old days.
The Chelsea Supporters' Trust were dismayed by the behaviour of fellow supporters on Tuesday.
The trust is right when it says that the actions of a few do not represent the club as a whole. That much is true, but the racially abusive men on that Paris Métro were Chelsea supporters. Neither the club nor the Chelsea Supporters' Trust denies that. Those supporters were, at the very least, representative of one element of the club's fan base. And that is a very uncomfortable reality for Chelsea in 2015.
Even those who follow the club home and away find it hard to identify a clear group who might be responsible for Tuesday's events but some say they recognise a tendency in a disparate number of fans in their twenties - young men - to revel in the notoriety they believe the club has attracted.
For a taste of just how abject some of the attitudes can be, an interview given to the Press Association by the 17-year-old Chelsea supporter Mitchell McCoy, who was identified after tweeting about the events on the Paris Métro, gives some idea.
"It wasn't just with the black people that we weren't letting them on," he said. "There was white people, women that people weren't allowing on. There was no space. They were saying, 'You can't get on this carriage, you have to go somewhere else'."
The club have been here before in recent years, albeit it in different circumstances, over the allegations of racism against John Terry in 2011. Acquitted in court the following year, he was charged by the Football Association and found guilty by an independent regulatory commission which worked to a lower burden of proof. The FA banned him for four games and fined him £220,000.
"Improbable, implausible and contrived" was the commission's verdict on Terry's account of how he came to say the words "f***ing black c**t" to Anton Ferdinand in a non-insulting context. Caught between the two verdicts - the commission and the court's - the club chose largely to ride out the storm. They said disciplinary action had been taken against Terry but never disclosed what it was. The matter was closed and to say it remains a touchy subject is putting it mildly.
Given that experience, it was no surprise that on Tuesday night a club tightly controlled by a small number of people answering to director Marina Granovskaia, and the ultimate boss, owner Roman Abramovich, were so swift in their response to the footage. They chose not even to wait until after the 45-minute flight back to London to issue a statement.
The images of the man in question being thrust backwards off the train by the fans inside the carriage are horrifying. First mystified, then angry, he tries to assert himself but is unable to resist the weight of numbers in the carriage. He is a black man being, so to speak, put in his place by a group of English football fans proud of their prejudices. Chelsea are well aware their new generation of global fans will watch keenly as to how the club react to the return of an unwelcome old problem.
For Chelsea and their global identity, the racial abuse by their fans filmed on that platform is poison