Pope Francis woke up in Dublin to the shock news that the man who was for three years his nuncio, or ambassador, to the United States had, overnight, called for his resignation for allegedly covering up sex abuse by Theodore McCarrick, the former US cardinal and ex-archbishop of Washington, DC.
(The 88-year-old McCarrick's unprecedented resignation as cardinal was accepted by the Pope in June after the emergence of credible abuse allegations against him when he was a priest in New York in the early-1970s. The Pope banned him from public ministry and ordered him to observe a life of prayer and penance in seclusion pending a canonical inquiry.)
No one can recall such a serious allegation against a pontiff, or such a brazen public attack on the authority of a pope from such an apparently credible and respected figure: former nuncio Archbishop Carlo Maria Vigano, a 77-year-old Italian.
He savaged the Pope in an explosive 11-page statement, or "testimony", as he called it, published in the National Catholic Register, a conservative Catholic newspaper/website in the US.
The statement, short on relevant detail and long on sweeping allegations and generalisations, coming hours before the Mass in Phoenix Park, appeared timed to cause the Pope maximum embarrassment.
No one who has followed the story closely can doubt that there is more to it than meets the eye.
The most serious allegation against Pope Francis - that he lifted sanctions that had been imposed on McCarrick by his predecessor, Benedict XVI - quickly collapsed, strengthening the suspicion that the whole thing is part of the ideological warfare in the Church between so-called liberals and conservatives; between those who support the emphasis on pastoral accompaniment and mercy stressed by Francis, as opposed to the rules-based "black-and-white" theology adhered to by many of his opponents, including possibly Vigano, and Francis's chief critic, Cardinal Raymond Burke, an American.
So, no wonder, then, that internationally respected newspapers, such as the Guardian, Financial Times and Economist, have responded to the story.
It is instructive to note some of the commentary which does not seem unfair in the circumstances.
The Financial Times said that "conservative opponents of Pope Francis are using widespread outrage over clerical cover-ups of sexual assault by priests to try to force his resignation".
The paper pointed out that Vigano targeted 32 other senior clerics, mostly "liberal allies of the Pope".
A Guardian editorial remarked that "the US Catholic Church is as completely divided by politics and culture as the rest of the country. The Catholic Right identifies with the Republican party almost as closely as parts of the evangelical movement do". The latest edition of the Economist says: "Like the rest of the country, the Catholic Church in America has become polarised."
It says conservative appointments by Francis's two predecessors turned the American Church "sharply to the Right, taking the Church even further from the traditions of social justice that Pope Francis is trying to restore".
Cutting away the polemic, there are two allegations by Vigano concerning Pope Francis that warrant interrogation.
Firstly, that he (Vigano), in 2013, told the Pope that the Vatican had a dossier on McCarrick who had "corrupted generations of seminarians and priests". And, secondly and more seriously, that Francis had lifted sanctions that Pope Benedict had imposed on McCarrick "in 2009, or 2010" that were "similar to the ones now imposed on him by Pope Francis".
Vigano said Francis "must be the first to set a good example for cardinals and bishops who covered up McCarrick's abuses and resign along with all of them".
These allegations created a sensation and Francis's response was the main story to emerge when journalists questioned the Pope on the flight back to Rome.
Pope Francis said that he had read the statement that morning. According to a translation, he told the journalists: "I must tell you sincerely ... and all those who are interested. Read the statement carefully and make your own judgment. I will not say a single word about this. I believe the statement speaks for itself. And you have the journalistic capacity to draw your own conclusions. When some time passes, and you have drawn your conclusions, I may speak. But I would like your professional maturity to do the work for you. It will be good for you."
One imagines that already some of the world's leading investigative journalists are on the case - the BBC's Panorama, maybe - responding to the papal challenge.
They will want to find out how McCarrick, made a cardinal by Pope St John Paul in 2001, climbed so effortlessly to the top of the greasy pole, even though a letter came to light at the weekend, via the Catholic News Service, showing that, in 2006, Archbishop (now Cardinal) Leonardo Sandri, then the number two in the Secretariat of State, acknowledged a complaint by Father Boniface Ramsey OP, a New York priest, made to the Vatican in 2000 about McCarrick's alleged sexual abuse of seminarians while Archbishop of Newark. The letter would seem to support Vigano's claim that the Vatican knew about allegations against McCarrick as early as 2000.
It's not surprising that Pope Francis, a Jesuit, has responded to Vigano with silence, even if he accepts that this may be an unsustainable stance in the longer term.
As one of his biographers, Austen Ivereigh, recounted on the Jesuits in Britain website last week, back in 1990, when during a period of "interior crisis" the future pope was exiled to Cordoba, in central Argentina, by the Jesuit leadership in Rome, because of his autocratic leadership style, he wrote an article Silencio y Palabra (Silence and Word).
Ivereigh says that, in it, the-then Fr Bergoglio suggested "a deeper spiritual purpose to his silence", namely a desire "to create space for God to act" drawn from a meditation on Christ's Passion in the Spiritual Exercises of St Ignatius of Loyola, the founder of the Jesuits.
Already, Vigano's claim that Benedict sanctioned McCarrick as Francis did has fallen apart.
McCarrick was a high-profile international churchman during Benedict's papacy and the former Pope's secretary, Archbishop Georg Ganswein, has said that reports that Benedict had "confirmed" Vigano's "testimony" were "fake news".
Vigano never complained about McCarrick's breach of supposed sanctions. He has declined to elaborate, or to be interviewed, and has gone into hiding.
Pope Francis will most likely weather the storm. He took resolute action against McCarrick, a noted fundraiser for the Church, unlike his two predecessors.
There is no real appetite in the Church for a second papal resignation in a matter of years. But the culture wars in the Church will continue.
So, too, will pressure on the Pope to apply stringent safeguarding norms worldwide and establish a standing court under canon law that will make it very difficult for sex predators, like McCarrick, to be protected and promoted.
Martin O'Brien is a journalist, communications consultant and award-winning former BBC producer