We know, of course, that all was not quiet at Kirk o'Field on that night. At 2 a.m. Darnley's lodging was blasted into rubble by a mighty explosion that was heard across the city, awakened most of its inhabitants, and initiated one of the greatest murder mysteries in history. For the chief victim was the King himself.

The reverberations from that explosion were keenly felt by those implicated in the plot, and they have been echoing down the centuries ever since. Controversy has raged over how Darnley died and who killed him, but the crucial question is whether or not Queen Mary was an accomplice in her husband's murder. She certainly had motives enough to want to be rid of him, but so, too, did several other people, including most of the Scottish nobility. And Darnley himself, incredible as it may seem, was not above suspicion.

Darnley's murder ultimately led to Mary's ruin. One factor was the convenient discovery of a box of documents - the notorious Casket Letters - that her enemies claimed were proof of her guilt. But Mary was never allowed to see the letters, and they disappeared in 1584. The question of their authenticity has haunted historians ever since.

After exhaustive re-examination of the source material, Alison Weir has found a solution to this enduring mystery that can be substantiated by contemporary evidence. In the process she shatters many of the misconceptions about Mary, Queen of Scots and produces an extraordinarily vivid portrait of Mary's Scotland at a great turning point in its history, when its future was so dramatically bound up with Elizabeth's England and when the destinies of two remarkable queens were fatally interlinked.