“The Lady in the Tower” glaringly omits any mention of Hilary Mantel’s “Wolf Hall,” this year’s Man Booker Prize-winning novel, which so ingeniously focuses on the machinations that made Thomas Cromwell the primary architect of Anne Boleyn’s destruction. Yet Ms. Mantel provides such a delectably arch portrait of Anne, and stints so deliberately on the clear historical details, that these two books serve as useful companion pieces. “Wolf Hall” is the more impenetrable. It is also the livelier by far.

“The Lady in the Tower” takes its title from one of the many, many pieces of evidence that Ms. Weir holds up for scrutiny. It comes from a letter of typically shady provenance, since much of the detail surrounding Anne’s undoing surfaced long after she had been undone. The letter is addressed “To the King from the Lady in the Tower,” and it first surfaced in 1649. Some have claimed it was copied by Cromwell from an original letter written by Anne on May 6, 1536, while she was imprisoned in the Tower of London. Historians have long debated the letter’s authenticity, and they have had ample reason to do so. Ms. Weir works hard to analyze not only the historians’ positions but also the essence of the letter itself.

In this instance, which is typical of the book’s approach, she sets forth various researchers’ thoughts about whether the letter was in Anne’s handwriting. Then she points out that Anne may have been so distraught that she needed to dictate, and that the handwriting issue may not be germane. (Besides, it might be Cromwell’s version.) Then she raises the question of why Cromwell would have held onto this document, “for why would Cromwell think it desirable to keep a letter from Anne protesting her innocence?” Most interesting, she notes that the “Lady in the Tower” locution is odd for a woman who regarded herself to be queen. And if Anne did not compose this letter, Ms. Weir wonders, who did?

Image Alison Weir Credit... Miklos Csepely-Knorr

Some of this book’s investigatory sojourns are far more palatable than others. The details surrounding the executions of Anne and her supposed lovers and co-conspirators are at least as ghastly as they are fascinating. What made beheading the most merciful form of execution? What made a sword a better implement for this than an axe? Why was an executioner summoned before the trial was even over? Did the sword have a groove to accommodate rivulets of blood? How long could Anne’s eyes and lips have kept moving after her head and body parted ways, and for how many seconds might she have suffered pain? It takes a hard-core monarchy enthusiast to appreciate Ms. Weir’s indefatigable pursuit of such information.