Described in this set are a number of secrets little known or completely unknown to Third Age humanity on Glorantha. The majority of the information has to do with the Elder Races of Glorantha.
Book 1 is the Secrets Book (51 pages) and covers a miscellany. The Inaccessible Glorantha sections give teasers about little known lands. The Unique Mysteries of Glorantha describes a number of mysterious features and objects that can be encountered around the world. The Secrets of Dragonkind section adds to the lore already revealed in other sources about the nature of Gloranthan dragons and their kin. Next up, stats are given for rare and unique creatures that powerful parties of adventurers might tackle. Treatments of Gloranthan geology, weather and the sky round out the book prior to a brief teaser about Heroquesting and the Hero Wars.
Book 2 is the Elder Races book (123 pages). The Mostali (Gloranthan dwarves), Aldryami (Gloranthan elves) and Uz (Gloranthan trolls) each get a detailed section including a cult listing. 19 more Elder Races get a thumbnail treatment and two more cults are introduced in the Lesser Elder Races section. Finally, scenario outlines involving the Elder Races are given.
A map showing concentrations of major Elder Races is also included in the box.