Mana from Heaven

In ancient times he was a powerful wizard known as the Phoenix. But much like oil and coal Mana, the fuel for magic, was a finite resource. Through the ages wizards have fought duels and nations have fallen protecting the limited supply of Mana. Only a handful of wizards have survived into modern days. These wizards keep their identities secret and hide from one another to keep the small amounts of Mana that they posses secret. But another wizard has been trying to kill Phoenix. He has to find out who it is and stop them before his entire supply of Mana is exhausted.
Roger Zelazny was a science fiction and fantasy writer, a six-time Hugo Award winner, and a three-time Nebula Award Winner. He published more than forty novels in his lifetime. His first novel, This Immortal, serialized in The Magazine of Fantasy and Science Fiction under the title ...And Call Me Conrad won the Hugo Award for best novel. Lord of Light, his third novel, also won the Hugo award and was nominated for the Nebula award. He died at age 58 from cancer. Zelazny was posthumously inducted into the Science Fiction Hall of Fame in 2010.
"A storyteller without peer. He created worlds as colorful and exotic and memorable as any our genre has ever seen." -George R.R. Martin
". . . his performance was never anything other than dazzling." -Robert Silverberg