Slatin was an Austrian officer in the service of the Egyptian government in the Sudan, who got caught up in the Mahdist rebellion. Leading the government forces in Darfur until forced to capitulate, he became a captive, and involuntary adviser, of the Mahdi. After being caught trying to communicate with the government forces in Khartoum he was for a while thrown in irons; being eventually pardoned he ended up in a curious position in the entourage of the Mahdi's successor, Abdullahi*. Valued for his knowledge of Egyptian affairs and European languages, as well as his watchmaking skills, he was also deeply mistrusted, because he was quite correctly suspected of lacking sympathy with the Mahdist cause, and of plotting to escape, which he finally did, with the help of the British and Austrian delegations in Cairo, in 1895, after twelve years' captivity. After the overthrow of the Mahdist state, he returned to the Sudan as an administrator in Anglo-Egyptian service until the First World War.

The book is a memoir covering the time from his stationing in the Sudan in 1879 until his escape in 1895. You can't accuse him of being an excellent writer, but it's an invaluable historical source and very interesting as an insider's view.

Towards the end of the book he makes some recommendations about how the outside world should act towards the Mahdist state; in short, he calls for invasion and reestablishment of Egyptian control. This is of course approximately what happened, and his appeal has been credited with swaying opinion in the British government towards action. He was quite wrong, however, in supposing that the Mahdist troops had lost their fanaticism and would not strongly defend Abdullahi's cause - in the event, they generally resisted Kitchener's forces with suicidal courage.

* Often known as "the Khalifa". The title means simply "Successor", sc. of the Mahdi, and is of course the same as "caliph", the title of Muhammed's successors. Why the older anglicization isn't used in the Mahdist case I do not know.