You have work to do when a biography is buttressed with four family trees. Such is Tudor history, complicated by Henry VIII's royal shenanigans in 1543, disinheriting Elizabeth (his daughter by Anne Boleyn) and Mary (his daughter by Catherine of Aragon).

The Grey sisters come into it because four years later Henry's will restored Elizabeth and Mary as next in line to the throne should Henry's son, Edward VI, die. Passing over the Stuarts -- always a pesky bunch of claimants -- Henry extended his line to the Greys, descendants of his younger sister, Mary Brandon, Duchess of Suffolk. Her granddaughters -- Jane, Katherine and Mary -- suddenly emerged as heirs to Elizabeth.

The first chapters of "The Sisters Who Would Be Queen: Mary, Katherine and Lady Jane Grey: A Tudor Tragedy," an ultimately fascinating book, are devoted to a bewildering menagerie of conniving Tudor nobles with a confusing collection of titles, family names and positions assembled around Edward VI, only 9 years old when his father died.

All the same, author Leanda de Lisle deftly dramatizes the dark, unintended, comic irony of Tudor times, with every nobleman swearing obedience to the king while attempting to make the monarch and court sway his own way. Thus you have the soap-opera seriousness of Jane's uncle, Thomas Seymour, First Baron Seymour of Sudeley, who married Catherine Parr, Henry VIII's widow. After her death, Sudeley proceeded to accost the teenage Elizabeth in her chamber while she cringed under her covers. Sudeley, so they said, schemed to marry the young princess. These foolish overtures to her ended in his public execution.

Meanwhile, Henry Grey, Marquess of Dorset, prepared his precocious daughter Jane for marriage to Edward VI. At 13, Jane could read and write Greek and Latin. Two years later she emerged alongside Elizabeth as the Protestant counterweight to Henry VIII's daughter Mary, a devout Catholic in a country divided over old and new ways of worship and prone to religious revolts verging on civil war.

By the spring of 1553, everyone at court seemed to know that Edward VI was dying, and the jockeying began with arranged marriages -- including Jane's to Guildford Dudley, son of Northumberland, head of Edward's Privy Council. By July, with the king dead, Northumberland engineered Jane's ascension to the throne, a 13-day affair that ended when Mary Tudor took power, ultimately (six months later) executing both Jane and her husband.

This extraordinary saga of what then happened to Jane's sisters -- both remained contenders to the crown, but were held firmly in check by the vigilant Elizabeth -- is well told, although their stories are too often wrapped in that biographer's dodge of what "must have been." In fact, their motivations remain shadowy or indecipherable, even with the padded details of their periods and political relations.

Carl Rollyson is a biographer and professor of journalism at Baruch College, the City University of New York.