DUFF, his long South African tour over, reached Scotland in July 1864, "with an enfeebled frame, and his face worn with pain and sleeplessness." His wife and children had preceded him. For a brief span he had rest, though now, as always, with spells of renewed activity. On 10th August, he addressed the Commission of the General Assembly; soon after he took part in Perth proceedings connected with the ordination of the Rev. W. Stevenson as a missionary to Madras; a little later he was at Haddo House, Aberdeenshire, welcomed there by the Countess of Aberdeen, for the ordination of another missionary to Madras. But after six months at home, he had to face the supreme trial of his life, the death of Mrs Duff. This was in February, 1865. The veteran missionary, writing to the son who had remained behind in India, referred to Mrs Duff as "my faithful, loving spouse—my other half, who sustained and cheered and comforted me, and was herself not merely the light of my dwelling, but my very home itself." He noted that in her last hours Mrs Duff had had no pain; that "life went gradually, gradually ebbing away. As there was no pain, you cannot imagine the singularly sweet, placid, and tranquil expression of her countenance even in the paleness of death." The letter breathed profound sorrow that "the union cemented by upwards of thirty-eight years of a strangely eventful life in many climes, and amid many perils and trials and joys," had been "so abruptly brought to a final close in this world," but the note of faith in a future re-union was triumphantly dominant.

The news of Mrs Duff's death caused deep regret in India. Nowhere was this regret more poignant than among the Bengalee Christians of Cornwallis Square, whose minister, the Rev. Lal Behari Day, speaking from the pulpit of the Mission Church, paid a moving tribute to the noble woman's memory. Mr Day had been twenty-two years a Christian, and he said that during this period he had not seen "a more high-minded and pure-souled woman of loftier character and greater kindliness. Her distinguished husband was engaged in a mighty work, and she rightly judged that, instead of striking out a path for herself of missionary usefulness, she would be doing her duty best by upholding and strengthening him in his great undertaking. Mrs Duff rightly judged that her proper province was to become a ministering angel to her husband, who was labouring in the high places of the field, who had to sustain greater conflicts than most missionaries in the world, and who, therefore, required more than most men the countenance, the attentions, the sympathy and the consolations of a loving companion. And it is a happy circumstance for our Mission and for India at large that Mrs Duff thus judged. The great success of the memorable father of our Mission is doubtless owing, under God, to his distinguished talents and fervent zeal, but it is not too much to say that that success would have been considerably less than it has been had his hand not been strengthened and his heart sustained by the diligent and affectionate ministration of his partner in life .....The angel of love who so long ministered to our reverent spiritual father, and who was his companion and solace in these wilds of heathenism, upholding his arms in the time of conflict, comforting him in distress, watching over him in sickness, and even pouring into his mind the balm of consolation—that ministering angel has been removed from his side, and Dr Duff has now, in the decline of his life, to pass the remainder of his days alone. What can we, his children on the banks of the Ganges, do further than express our profoundest sympathy with him, and commend him to the fatherly care of Him who is emphatically the God of all comfort?