[Source: ‘Collected Letters of St. Therese of Lisieux,’ Translated by F.J. Sheed, The Catholic Book Club, London, 1974]
Two Letters of St. Therese to her sister, Celine:
“He wants His little Flower to save Him souls, and for that He wants only one thing, that His flower should look at Him while it suffers its martyrdom… and this mysterious gaze passing between Jesus and His small flower will work marvels and will give Jesus a multitude of other flowers, particularly a certain faded, withered lily [Fr. Hyacinthe] that must be changed into a rose of love and repentance.” (26 April 1891)
“Dearest Celine, he is indeed guilty, more guilty perhaps than any sinner has ever been who was yet converted; but cannot Jesus do what He has never done before? And if He did not wish it, would He have put into the heart of His poor little brides a desire He could not fulfil? … No, it is certain that He desires more than we to bring back this poor lost sheep to the fold; a day will come when he will open his eyes…” (8 July 1891)
Fr. Hyacinthe
“Hyacinthe Loyson died in Paris 9 February 1912, at the age of eighty-five, under major excommunication. He was assisted at the end by a priest of the Armenian Church, a representative of the schismatic Greek Church, and three Protestant pastors. It is worth observing that the poor erring creature had never ceased to repeat the invocation: ‘O my sweet Jesus.’ Therese, who had prayed for him throughout her religious life, offered her last Communion for him, in 1897, on 19 August, which at that time was the feast day of St. Hyacinthe.”
Details given under all reserves to the Lisieux Carmel:
From the abbey of St. Maurice at Clervaux (19 August 1912):
“At the moment of the unhappy man’s death, a privileged soul saw him supernaturally enlightened upon the whole extent of the sins of his life. This sight was the occasion of a terrifying temptation to despair over which, happily, he triumphed.”
From Pere Flamerion, S.J., grand exorcist of France (25 August 1912):
“You have asked us in the Virgin’s name if Hyacinthe is damned; we are forced to answer you that he is saved, through the intercession of Therese and the prayer of holy souls in the cloister, saved by a glance cast upon him by Our Lord before he was judged, an instant before.”
‘His hands are turned and as of gold, full of hyacinths.’
– Cant. 5:14
Littlest Souls 
That was my reaction also! I discovered part of the story in another book, but the words of the demon(s) were attributed to the exorcist. An unfortunate error.
Absolutely! Imagine what Our Lady’s confidence must be!
A blessed Feast of the Immaculate Conception to you, Pat!
I had never read this story before — wonderful!! “ He have put into the heart of His poor little brides a desire He could not fulfil?“ I love these words from Therese! Confidence!