BLACK TRILLIUM, the first of this 5-book "series", was written by 3 cooperating authors, about 3 princesses protecting their country against sorcerers & hostile invasion, with the help of 3 magic talismans. Then the authors went their own ways with individual stories, still set in the World of Three Moons. May wrote BLOOD TRILLIUM and its own sequel, SKY TRILLIUM, continuing the story of all 3 princesses. BLOOD TRILLIUM is set 12 years after BLACK TRILLIUM.
Details in GOLDEN TRILLIUM (by Norton) and LADY OF THE TRILLIUM (by Bradley) contradict details in May's books, but GOLDEN TRILLIUM follows the story of Princess Kadya, and LADY OF THE TRILLIUM follows the story of Princess Haramis. So ... you actually have 3 series here ... all starting with BLACK TRILLIUM, and all of them following the story of one or more of the 3 princesses featured in the original book.
12 years past, the sisters Haramis, Kadiya and Anigel wielded the three-part Sceptre of Power to restore balance to a world threatened by the sorcerer Orogastus. Now, amid portents of new danger, the Archmage Haramis is visited by a fugitive who brings dire news. A sorcerer marooned on the remote island called the Land of Fire and Ice has escaped, overthrowing the ruler of a small nation to establish himself as Portolanus, Master of Tuzamen.
Is Portolanus in truth Orogastus, long ago banished by the Sceptre? Will his power disrupt the peace between the world's peoples and also tear the sisters asunder?
BLOOD TRILLIUM continues the richly woven saga of magic and power created by 3 of fantasy's most brilliant minds
A dozen years after the events recounted in Black Trillium , the World of the Three Moons is endangered by another sorcerer, Portolanus, Master of Tuzamen, considered a mountebank by some, yet still dangerous. The three sisters who hold the talismans of the Sceptre of Power, which previously saved their country, Ruwenda, must bury their differences to save their world. When Kadiya, the middle sister, champion of the aborigines, loses her talisman, and Portolanus and the pirate queen of Raktum kidnap the king of Laboruwenda and his children to obtain the talisman of his wife, the queen, it remains for Archimage Haramis, the oldest sister, to master her powers sufficiently to take on Portolanus and the armies he has raised against her beleaguered country. The Master of Tuzamen is no longer a figure of fun, however, but is unveiled as Orogastus--the powerful and evil sorcerer, believed destroyed 12 years previously. This sequel to the joint effort produced by May, Andre Norton and Marion Zimmer Bradley is a superior tale, giving life, character and emotion to the three Petals of the Living Trillium as they continue their adventures.