COLORFUL, SWAGGERING, glamorous and cunning, the Tudor monarchs still have a potent fascination for us all. Even the sickly boy-king Edward VI and the cold, careful Henry VII have their admirers; as for Henry VIII and Elizabeth I, there seems no end to the books about them.

Mary I is another matter. The elder daughter of Henry VIII and his Spanish queen, Katherine of Aragon, she clung tenaciously to the Old Faith through all the upheavals of the Reformation, and when she came to the throne, rather unexpectedly, on her brother's death in 1553 she did her best to put the clock back. She not only returned the nation to the Roman obedience and married Philip II of Spain, she burnt nearly 300 Protestants under the medieval heresy laws; and the cruelty and glory of their martyrdom was perpetuated over the next two centuries by John Foxe's Acts and Monuments (better known as "Foxes's Book of Martyrs"), which proved a spectacular best seller.Worse still, she failed. Failure was something the Tudors did not recognize, and something posterity rarely forgives.On her death in 1558 at the age of 46, childless, prematurely old and deeply embittered, the crown passed to her half-sister Elizabeth, who threw in her lot with the Protestants and left them to rewrite the history books. Religious bigotry depressed Bloody Mary's reputation right into the 19th century, and in a more liberal age hostility has only degenerated into mild contempt, or pity.

There have been attempts at understanding, of course, if not rehabilitation. The best of them is H. F. M. Prescott's Spanish Tudor, in 1940, a sensitive character study from a mildly revisionist, Catholic point of view. (In fact, even her coreligionists have been disenchanted with her, because of the damage she did to the Catholics in England.) Now comes Carolly Erickson, with the first full-length study which tries to do full justice to her, written with sympathy but without prejudice.

It is a big, energetic, entertaining book, a book of considerable literary distinction, with great narrative drive. I suspect that some of Erickson's setpieces owe their detailed color to her imagination, but her training as a professional historian keeps the main structure of the story firmly tied to the evidence. She has sifted and re-examined this evidence, in the form of memoirs, dispatches, state papers, and letters, with great thoroughness. The result commands belief as well as respect, and long as it is, I do not think any reader at all interested in the 16th century will find it too long.

Erickson's great strength is that she deals fully with Mary's life before her accession; indeed, her five-year reign is for once set in proper proportion, occupying less than a quarter of the book. Without venturing into amateur psychology, she exposes and analyzes the tensions created by an upbringing which was irrational and unnatural even for a princess of the blood royal.

In fact, all went well until Mary was in her teens. She was born in 1516, the first child of Henry VIII and Queen Katherine. Assuming the eventual arrival of a younger brother, she could look forward to the artificial but luxurious life of a great lady, perhaps even a queen consort somewhere in Europe; through her mother she was the cousin of the great Holy Roman Emperor Charles V, and Henry VIII was not a father to be despised. But in 1529 her world began to fall apart. Her mother bore no further children, and Henry decided that the accession of a queen would threaten the stability of the monarchy. To get his divorce, and marry Anne Boleyn, he had to pull the whole nation away from Rome; this was in 1532. Katherine of Aragon refused to accept the divorce; even less the break with Rome, and at the age of 18 Mary found herself condemned with her mother to a life of isolation and comparative penury in remote country houses, constantly supervised, constantly watched, and subjected to unrelenting pressure to change her religion. As the focus for Catholic and loyalist plotting against the king, her life was in real danger; an increasingly ogreish Henry VIII soon executed Anne Boleyn, and in 1542 he executed his fifth wife, Catherine Howard, without much ado. Worse still, Mary was bastardized by Act of Parliament and barred from the succession, even after the birth of her half-brother, the future Edward VI, in 1537. There could be no question of her marriage; in fact, she was isolated from men of her own age. After her mother's death in 1536 she was increasingly lonely, frustrated and frightened.

But, as Erickson points out, through it all she continued to revere and respect her father; with all his iniquities he was a great king, and he remained "her benchmark of political power" to the very end. Encouraged by the unanimity with which she was swept to the throne, in defiance of alternative Protestant candidates, she set out to emulate her father, which was impossible, and worse still, to correct his "mistakes." Henry VIII, she thought, had always remained true to the Old Faith as he understood it (though this was an important qualification), and his sole error, from which all else stemmed, was his break with Rome.

True, the Protestant Reformation under Edward VI had been put through in a hurry, and its roots were shallow; provided their possession of confiscated church lands was confirmed, the nobility and gentry were willing enough to resume the Catholic faith. The religious situation was fluid, and Mary might have effected a Catholic-based compromise, just as Elizabeth I negotiated a Protestant-based compromise. What the upper classes would not accept was a headlong return to the Roman obedience, bringing with it wholesale interference by ultramontane churchmen like Cardinal Pole and intolerant religious persecution on a scale not seen before in England.Still less were they prepared to tolerate a royal marriage which would make England an appendage of Spain, or even, in the next generation, a mere province of the Spanish world-empire. Mary's point-blank refusal to marry a suitable Englishman, like Edward Courtenay, Earl of Devon, is strange; her father had set an example by marrying four English wives out of six. (Elizabeth I, it is true, refused to marry a subject, but nor would she marry a foreign prince.)

In other words, I think it was the nature of Mary's Catholicism rather than the mere fact of it which proved her bane, and Erickson, in the pursuit of her narrative, has not left herself enough room for this kind of analysis - though, of course, she might not agree with it. But it remains, as I have said, a distinguished and highly readable book.