The title here gives it all away: this is a depiction of the human slave trade in east Africa around the time it was becoming abolished (according to the narration), circa 1884. This picture followed in the wake of the phenomenal "Roots" TV mini-series of '77, along with other international productions of the period, such as "Ashanti." It's not very well known by this time and barely seen anywhere, an example of exploiting the slavery angle prevalent during the seventies, but seemingly based on historical fact.

The movie utilizes well-known actors (Trevor Howard, Ray Milland) and TV's Tarzan (Ron Ely) as the nominal hero, who starts out as a typical bigot of that era but progresses to sympathetic status near the conclusion. Most of the plot has to do with competing slavers fighting over the dwindling slave trade; this trade is technically outlawed by this point, but continues under those unwilling to give it up (it's highly profitable, after all). There's a central set piece of a slaver's home base invaded by servants of a competitor, for example, resulting in some bloody violence.

The movie contains scenes of stark, callous brutality, emphasizing that most aristocrats during that time considered dark-skinned people as lower than human. A particularly shocking scene is overseen by the most powerful slaver (Milland), who casually shoots slaves in a pond as entertainment for his upper class guests, who clap appreciatively at his marksmanship. This drives home the point that in the 19th century the mindset was quite different. Yet, Ely's character is temporarily placed in bondage as well, despite obviously being a blond Nordic type; perhaps at this time, slavers were less discriminating due to the reduction of opportunity in this area. The incident serves to awaken the tall blonde fellow's humanity. Howard hams it up as another competing slaver (and Ely's uncle), who appears to be less of a monster than most, but the picture eventually reveals that all involved in such evil enterprise are by necessity inhuman sadists when all's said and done, and there are no happy endings.