Plot summary
In the previous book, Merlin Book 9: The Great Tree of Avalon, the evil sorcerer Kulwych made a pure crystal of élano out of the water from the White Geyser of Crystillia. Élano is the most powerful substance in Avalon and is known for its power to create life. At the beginning of Shadows on the Stars, the wicked spirit Rhita Gawr corrupted this pure crystal of élano and thereby transformed into an anti-matter-like version of itself, called vengélano, which destroys whatever it touches.
Facing this danger, the three young heroes, Tamwyn, Elli, and Scree, must push their abilities to their limit to save Avalon. Tamwyn must somehow find and relight the darkened stars of the constellation Wizard's Staff. Elli must seek the crystal of vengélano and destroy it. Scree must confront his greatest mistake, which nearly cost him his life and the staff of Merlin, to help defeat Rhita Gawr's army.
Tamwyn, accompanied by Henni the hoolah and the small, winged creature called Batty Lad, leaves Avalon's root-realms – the seven familiar sections of Avalon, home to the greatest diversity of lifeforms – and enters the trunk and is separated from his friends. He discovers, among other things, growth rings of the Tree that tell its history; places where giant termites dwell; and the Ayanowyn, whose once glorious society has become a dystopia. When living with the Ayanowyn, Tamwyn learns that if a wreath of mistletoe were to appear among them, the one to whom it appeared would become their leader. While leaving the Ayanowyn to continue his travels, Tamwyn finds such a wreath and leaves it with his former host.
Because, as a rule, humans think of trees as being wooden, the description of Avalon's trunk as being essentially made of stone and consisting of such topography as exists in our real world creates some ambiguity. In Avalon's tree-world, a knothole becomes a valley, and the outside of the trunk becomes similar to a cliff, or to Amara, though Avalon's surface is less steep than Amara's.
In or near Merlin's Knothole, Tamwyn meets Ethaun, a blacksmith and the sole survivor of his father Krystallus' expedition to the stars. Ethaun shelters Tamwyn, reforges Tamwyn's broken dagger, brings him to visit Krystallus' grave, and gives him a globular compass. Tamwyn eventually discovers the stars that illuminate Avalon, occupying the niche held by the Sun in our world, and the niche held by the stars of our night sky, are "doors of fire" that lead to other worlds including ours and the spirits' Otherworld. To rekindle the constellation Wizard's Staff, Tamwyn must shut the doors of which it is made.
Elli, accompanied by Nuic, Shim, Brionna, and a priest of the order to which Elli belongs, called Lleu, seek the aid of the water dragons. When the aid comes slowly, they leave via the portals that link the seven root-realms; mistakenly to the realm Malóch, where they learn that Elli's former tormentor Llynia is part of a eugenic, genocidal effort to impose human rule. Escaping from Llyina's clutches with the help of a gnome whose life Elli had saved in the previous book, they continue with greater urgency.
In a dream created by Tamwyn's magic, he and Elli meet on a cloud. There he gives her a half-finished harp in replacement of the one he broke. In exchange, they kiss.
Scree returns to Rahnawyn, the realm of his birth and learns eaglefolk clan called Bram Kaie is destroying other eaglefolk. Having experienced their cruelty firsthand, Scree attacks the renegade clan alone. He has previously met their leader, Quenakhya, who had seduced Scree to seize the magic staff Ohnyalei. When he understood this, Scree had fled. On returning, he watches as Quenakhya's son challenges and kills her for leadership. Scree immediately challenges and kills him. On her last breaths, the dying Quenakhya reveals that Scree is the father of the warrior whom he has slain. Ashamed of himself, but cognisant of necessity, Scree takes the leadership of Bram Kaie.
