An early novel. Her prose style is still evolving, and you can see some other implications, but still entrancing.
Three generations of wizards have lived on a mountain and summoned marvelous, legendary beast -- a dragon, a boar that asks riddles -- and Sybel, the heroine, is the third generation. Her attempts to summon a marvelous bird are interrupted by a man, who had just survived a fierce battle, bringing her a baby. The son of her mother's youngest sister (her father had summoned her mother, a princess, too). Coren persuades her to take Tamlorn, and with the help of Maelga, the local witch, she manages to raise him. But he is also the son of a king.
Coren returns, and tells Tam of his origin. The conflicts of the kingdoms enter her world, and her powers to affect them mean she is drawn in.
It involves a dragon reclaiming its treasure, Sybel's summoning Tam's father twice, a wizard making Sybel an offer, a monstrous beast that tells Sybel she summoned it, and much more