Having brought back a mysterious rock from his expedition to the South Pole, Mortimer is soon put on the trail of a fantastic civilization whose cradle seems nestled in the entrails of the Ngorongoro crater, not far from Lake Victoria. Then begins a sumptuous African adventure that will lead for the first time our two heroes to Black Africa and Tanganyka (present-day Kenya and Tanzania). With this great return of the two most famous gentlemen of the comic strip, Yves Sente and André Juillard sign a thriller that will surprise and delight more than one lover of this mythical series and great adventure in general.