Harry Potter froze in terror as the hellish Dementors rushed to suck out his godfather's soul. But he was not powerless, because he had learned the Patronus Charm for use against the evil ones. So the boy wizard focused on a joyful memory and shouted, "Expecto Patronum!"

Salvation arrived in the form of a dazzling silver animal that defeated the ghouls and then cantered across the surface of a lake to Harry. It was as "bright as a unicorn," but on second glance was not a unicorn. It was a majestic stag that bowed its antlered head in salute and then vanished.

If C.S. Lewis or J.R.R. Tolkien had written this scene in "The Prisoner of Azkaban," literary critics and Christian apologists would know how to break the code, according to John Granger, author of "The Hidden Key to Harry Potter." They would parse the Latin charm and study author J.K. Rowling's delicate use of medieval symbolism.

"The key is that stag, which is often a Christ symbol. But she is not content to make it a stag. It's a stag that looks like a unicorn," said Granger, who teaches Latin and Greek in Port Hadlock, Wash.

"She's saying to the reader, 'A stag may be a reach for you. So I'll have it be a stag that looks like a unicorn, since that has been a universally recognized Christ symbol for ages.' It's almost, 'Let me make this clear for you.' "

But these symbols have eluded most readers who have bought 192 million copies of these novels in 55 languages. (Rowling requested Latin.)

This weekend bookstores are serving up the first 8.5 million copies of the 768-page fifth volume, "Harry Potter and the Order of the Phoenix." The usual suspects will immediately say the usual things. Many Christians will quote Bible verses condemning magic. Academics will call the book a childish confection and analyze it as media myth and pop psychology. Librarians will give thanks that children are reading -- anything.

Granger believes they are missing the obvious: Rowling has baptized her work in medieval Christian symbols and themes that shape and define her tales of good versus evil. Potter's creator, he noted, received a superior education -- with studies in French and classical languages at the University of Exeter -- and has a working knowledge of ancient and medieval literature. She has made no effort to hide her admiration of great writers, especially Jane Austen and Lewis.

Granger has focused on her language and symbolism, in large part because of his similar studies in "Great Books" and ancient languages. He has also attempted to predict how these themes will play out in Rowling's future Potter novels.

"I started reading the Potter books as an Orthodox Christian father who had to explain to his oldest daughter why we don't read such trash," he said. "But once I started turning the pages the University of Chicago side of me kicked in."

Take that climactic scene in "The Prisoner of Azkaban," he said. The Latin "expecto," as used in the Apostles' Creed, is best translated "to look out for" or "to long for expectantly." And "patronus" means guardian, but can also mean "deliverer" or "savior." So Potter cries "I look for a savior" and a stag appears, one that looks mysteriously like a unicorn.

In the Middle Ages, noted Granger, stags were Christ symbols, in part because of the regeneration of their antlers as "living trees." A cross was often pictured in the prongs. Lewis uses a white stag in this manner in "The Chronicles of Narnia." Unicorns were also popular Christ symbols, portraying purity and strength.

Rowling repeatedly links Potter with creatures -- a phoenix, griffins, centaurs, hippogriffs, red lions -- used by centuries of Christian artists.

Her use of alchemy symbolism taps into medieval images of spiritual purification, illumination and perfection.

None of this is accidental, he said. Anyone who cares about Potter-mania must take Rowling more seriously.

"What we are seeing is a religious phenomenon taking place in a profoundly secular, profane culture," said Granger. "J.K. Rowling is pouring living water into a desert. ... She is mounting a head-on attack on a materialistic world that denies the existence of the supernatural and, so far, she is getting away with it."