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.

The founding of the Mission had been a romance. It was not from Scotland that the impulse came but from Jamaica in the West Indies. The slave population of that colony had been brought from the West Coast, and chiefly from the Calabar region, and although ground remorselessly in the mill of plantation life they had never forgotten their old home. When emancipation came and they settled down in freedom under the direction and care of the missionaries their thoughts went over the ocean to their fatherland, and they longed to see it also enjoy the blessings which the Gospel had brought to them. The agents of the Scottish Missionary Society and of the United Secession Church, who, together, formed the Jamaica Presbytery, talked over the matter, and resolved to take action; and eight of their number dedicated themselves for the service if called upon. A society was formed, and a fund was established to which the people contributed liberally. But the officials at home were cold; they deprecated so uncertain a venture in a pestilential climate. The Presbytery, undaunted, persevered with its preparations, and chose the Rev. Hope M. Waddell to be the first agent of the Society.

It is a far cry from Jamaica to Calabar, but a link of communication was provided in a remarkable way. Many years previously a slaver had been wrecked in the neighbourhood of Calabar. The surgeon on board was a young medical man named Ferguson, and he and the crew were treated with kindness by the natives. After a time they were able by another slaver to sail for the West Indies, whence Dr. Ferguson returned home. He became surgeon on a trader between Liverpool and Jamaica, making several voyages, and becoming well known in the colony. Settling down in Liverpool he experienced a spiritual change and became a Christian. He was interested to hear of the movement in Jamaica, and remembering with gratitude the friendliness shown him by the Calabar natives he undertook to find out whether they would accept a mission. This he did through captains of the trading vessels to whom he was hospitable. In 1848 a memorial from the local king and seven chiefs was sent to him, offering ground and a welcome to any missionaries who might care to come, This settled the matter. Mr. Waddell sailed from Jamaica for Scotland to promote and organise the undertaking.

Happily the Secession Church adopted the Calabar scheme, and after securing funds and a ship—one of the first subscriptions, it is interesting to note, was £1000 from Dr. Ferguson—Mr. Waddell, with several assistants sailed in 1846, and after many difficulties, which he conquered with indomitable spirit and patience, founded the Mission. In the following year it was taken over by the United Presbyterian Church, which had been formed by the union of the United Secession and Relief Churches.

In no part of the foreign field were conditions more formidable. Calabar exhibited the worst side of nature and of man. While much of it was beautiful, it was one of the most unhealthy spots in the world— sickness, disease, and swift death attacking the Europeans who ventured there. The natives were considered to be the most degraded of any in Africa. They were, in reality, the slum-dwellers of negro-land. From time immemorial their race had occupied the equatorial region of the continent, a people without a history, with only a past of confused movement, oppression, and terror. They seem to have been visited by adventurous navigators of galleys before the Christian era, but the world in general knew nothing of them. On the land side they were shut in without hope of expansion. When they endeavoured to move up to the drier Sahara and Soudanese regions they were met and pressed back by the outposts of the higher civilisations of Egypt and Arabia, who preyed upon them, crushed them, enslaved them in vast numbers. And just as the coloured folk of American cities are kept in the low-lying and least desirable localities, and as the humbler classes in European towns find a home in east-end tenements, so all that was weakest and poorest in the negro race gravitated to the jungle areas and the poisonous swamps of the coast, where, hemmed in by the pathless sea, they existed in unbroken isolation for ages. It was not until the fifteenth century that the explorations of the Portuguese opened up the coast. Then, to the horrors of the internal slave-trade was added the horror of the traffic for the markets of the West Indies and America. Calabar provided the slavers with their richest freight, the lands behind were decimated and desolated, and scenes of tragedy and suffering unspeakable were enacted on land and sea. Yet for 400 years Europeans never penetrated more than a few miles inland. Away in the far interior of the continent great kingdoms were known to exist, but all the vast coastal region was a mystery of rivers, swamps, and forests inhabited by savage negroes and wild beasts.

It is not surprising that when the missionaries arrived in Calabar they found the natives to have been demoralised and degraded by the long period of lawlessness and rapine through which they had passed. They characterised them in a way that was appalling: many seemed indeed to have difficulty in selecting words expressive enough for their purpose. "Bloody," "savage," "crafty," "cruel," "treacherous," "sensual," "devilish," "thievish," "cannibals," "fetish-worshippers," "murderers," were a few of the epithets applied to them by men accustomed to observe closely and to weigh their words.

Not an attractive people to work amongst. Neither must the dwellers of the earth have appeared to Christ when He looked down from heaven ere He took His place in their midst. And Mary Slessor shrank from nothing which she thought her Master would have done: she rather welcomed the hardest tasks, and considered it an honour and privilege to be given them to do. She was not blind to the conditions at home. Often when at the Mission she realised how great was the need of the slums, with their problems of poverty and irreligion and misery. But the people there were within sight of church spires and within hearing of church bells, and there were many workers as capable as she: whilst down in the slums of Africa there were millions who knew no more of the redemptive power of Christ than did the beasts of the field. She was too intelligent a student of the New Testament not to know that Christ meant His disciples to spread His Gospel throughout the world, and too honest not to realise that the command was laid upon every one who loved Him in spirit and in truth. It was therefore with a quiet and assured mind that she went forward to the realisation of the dream. She told no one: she shrank even from mentioning the matter to her mother, but patiently prepared for the coming change. In the factory she took charge of two 60-inch looms, hard work for a young woman, but she needed the money, and she never thought of toil if her object could be gained.

Early in 1874 the news of the death of Dr. Livingstone stirred the land: it was followed by a wave of missionary enthusiasm; and the call for workers for the dark continent thrilled many a heart. It thrilled Mary Slessor into action. She reviewed the situation. Her sisters were now in good situations, and she saw her way to continue her share in the support of the home. What this loyal determination implied she did not guess then, but it was to have a large share in shaping her life. Broaching the subject to her mother she obtained a glad consent. One or two of her church friends were lukewarm; others, like Mr. Logic and Mr. Smith, encouraged her. The former, who was deeply interested in foreign missions and soon afterwards became a member of the Foreign Mission Committee, promised to look after her affairs during her sojourn abroad.

In May 1875 she offered her services to the Foreign Mission Board. Her heart was set on Calabar, but so eager was she to be accepted that she said she would be willing to go to any other field. Women agents had long been engaged in Calabar. The first, Miss Miller, had gone out with Mr. Waddell in l849-she became the "Mammy" Sutherland who did such noble service-and they were playing an ever more important part, and were stated to be both "economical and effective." Requests had just been made for additions to the staff. The application was, therefore, opportune. Her personality, and the accounts given of her character and work, made such an impression on the officials that they reported favourably to the Board, and she was accepted as a teacher for Calabar and told to continue her studies in Dundee. In December it was decided to bring her to Edinburgh, at the expense of the Board, for three months, for special preparation….

The night before she left Dundee, in March 1876, she stood, a tearful figure, at the mouth of the "close" where she lived. "Good-bye," she said to a friend, and then passionately, "Pray for me!"