There was never a time when Mary was not interested in foreign missions. The story of Calabar had impressed her imagination when a child, and all through the years her eyes had been fixed on the great struggle going on between the forces of light and darkness in the sphere of heathenism. The United Presbyterian Church in which she was brought up placed the work abroad in the forefront of its activity; it had missions in India, China, Jamaica, Calabar, and Kaffraria; and reports of the operations were given month by month in its _Missionary Record_, and read in practically all the homes of its members. It was pioneer work, and the missionaries were perpetually in the midst of adventure and peril. Their letters and narratives were eagerly looked for; they gave to people who had never travelled visions of strange lands; they brought to them the scent and colour of the Orient and the tropics; and they introduced into the quietude of orderly homes the din of the bazaar and harem and kraal. These men and women in the far outposts became heroic figures to the Church, and whenever they returned on furlough the people thronged to their meetings to see for themselves the actors in such amazing happenings, and to hear from their own lips the story of their difficulties and triumphs.
Mrs. Slessor never missed hearing those who came to Dundee, and once she was so much moved by an address from the Rev. William Anderson as to the needs of Old Calabar that she longed to dedicate her son John to the work. He was a gentle lad, much loved by Mary. Apprenticed to a blacksmith, his health began to fail, and a change of climate became imperative. He emigrated to New Zealand, but died a week after landing. His mother felt the blow to her hopes even more than his death. To Mary the event was a bitter grief, and it turned her thoughts more directly to the foreign field. Could she fill her brother's place? Would it be possible for her ever to become a missionary? The idea floated for a time through her mind, unformed and unconfessed, until it gradually resolved itself into a definite purpose. Sometimes she thought of Kaffraria, with its red-blanketed people, but it was always Calabar to which she came back: it had from the first captivated her imagination, as it for good reason captivated the imagination of the Church.