How friend-turned-foe gave the Pope a rude awakening
It was a quiet weekend for the Pope. The Malta visit went off not badly, flying in, volcanic ash and all. The London Sunday papers were mild enough, considering. Two of them consigned the visit to page 28, cheek by jowl with the crossword, the weather and the TV.
Almost completely ignored, as if it was a torpedo silently homing under the placid blue waters of the Med, was the open letter from a German theologian.
Addressed to the Catholic bishops of the world, it went also - bitingly - to the Bishop of Rome.
Kung is its author - Hans Kung (below): not a name to conjure with in the headlines of the tabloids, or on the television news.
But among those on the inside track, a weighty name of great brilliance, insight and, among theologians, of unique integrity.
Kung has always been a rebel ready to rock the boat. His search has been for the truth.
As young men, Ratzinger and he were radical colleagues on the faculty of the 15th century University of Tubingen near Stuttgart.
But Ratzinger, the one-time poacher, brought to Rome, soon turned gamekeeper.
As John Paul II's henchman, he was charged with keeping the bishops and theologians in line.
For 25 years he ran the Congregation for the Doctrine of the Faith - the Vatican's enforcement office - for John Paul.
Until Vatican II in 1962, it had been known by its old name, the Holy Office of the Inquisition. When Ratzinger took over, critics observed tartly he ensured that only the name had changed.
John Paul was no administrator. He trusted Ratzinger and left him to get on with it, while he went on his travels as a means of escape from the curia.
Everyone knew that, under John Paul, nothing happened without Ratzinger's approval. It was a remarkable collaboration when one considers how savagely the invading Wehrmacht had behaved to the Poles in 1939.
When John Paul died in 2005, virtually all the electing cardinals knew they owed their places to the German, who so badly wanted to be Pope.
But Kung, the brilliant Swiss from the placid shores of Lucerne, the church's greatest living theologian, was not to be silenced.
A week before Christmas in 1979, just after John Paul's elevation, Ratzinger put him under Vatican edict, which meant he lost his teaching chair.
Summoned to Rome, Kung refused to go. He received 10,000 letters, nine out of 10 supporting his stand for church reform: a married priesthood; women priests; the use of condoms to curb over-population and HIV in Africa; less absolutism from Rome; more consultation with the bishops.
Kung was swiftly given another university chair by Tubingen. He travelled the world. He came to Ireland and appeared before packed audiences.
I talked to him for an hour in Dublin for a broadcast interview. He condemned Protestant bigotry in Northern Ireland.
Both Protestants and Catholics would have to change if they wished to solve the community problem as his native Swiss had done. "We should not wait for the day when our churches are nearly empty," he told me, "before proceeding to inter-communion."
He had a private conversation - lasting four hours - with the new Pope, shortly after Ratzinger assumed office.
Now, in his open letter, he has said it all again: "Venerable bishops, Pope Benedict XVI and I were the youngest theologians at the Second Vatican Council . . . Now we are the oldest and the only ones still fully active . . . I am making this appeal to you . . . motivated by my profound concern for our church, which now finds itself in the worst credibility crisis since the Reformation . . ."
What follows is a devastating demolition of Benedict's deeds as Pope, condemning him for missed opportunities and for personally engineering previously, as John Paul's chief executive, the worldwide cover-up of the sexual crimes of priests.
Kung's is a desperate cry. But it may already be too late to avoid a tortuous ordeal of victims' litigation and of inquest, diocese by diocese, which now faces the church.
Popes do not resign. But, before the agony is finished, Benedict may wish that they did.