When Dr William Macbeth poisoned two of his sons in 1927, the secret remained buried. But secrets can be as corrosive as poison, and the story of Macbeth haunted his descendants. Macbeth's granddaughter, Gail Bell, is determined to understand Macbeth's life, and she turns to the great poison cases of history and fiction. Beautifully written, with a stunning twist at its end, THE POISON PRINCIPLE is both a fascinating detective story and a moving memoir of death and deceit. 'Miraculously well written, compellingly readable . . . a book of rare distinction' THE TIMES '[Bell's] solution to the mystery was - and is - a triumph of perseverance . . . enthralling' GUARDIAN'Beautifully written' SUNDAY TIMES