Delving through the poison

Twenty-two years ago, Gail Bell managed to persuade one of her elderly relatives to recount a story that had haunted her family since the late 1920s. Was it true, she wanted to know, that her grandfather had really poisoned two of his four sons?

Rose Clark, Bell's great-aunt and sister-in-law of her late grandfather William Macbeth, told everything: of Macbeth's dandyish taste in clothes; of his success as a "herbalist and botanist, dispenser and medical masseur"; and how, finally, he had murdered the two boys - one of whom was "hopelessly retarded", and the other whose only crime was to have "trespassed in the dispensary" - with strychnine.

At the time, Bell was 30, and a pharmacist, and accepted the veracity of the story, even if she recognised that there might have been an element of score-settling in the elderly Clark's decision to spill the beans. As the years passed, however - and her professional knowledge of chemistry and poisons grew - she became increasingly hungry to excavate the whole story.

She, unlike Clark, was of the same blood as Macbeth; she wanted to "see the man in the monster".

Finding the truth about her grandfather - whose business cards promoted him as "late of Pennsylvania, USA", more recently a successful travelling faith healer in New South Wales - is not easy, and Bell's investigations take her into territory both literary and criminal, medical and psychological.

The resulting book - The Poison Principle, already a best seller in her native Australia - is a complex weave of these themes. It is also a subtle meditation on the nature of family, and the secrets and lies that colour our relationships with those closest to us.

Poison, in Bell's hands, is a beast of many faces. It is, to some, the perfect method of suicide: a few days before she took her life, Eva Braun told Frau Junge, Hitler's secretary: "I want to be a pretty corpse. I'm going to take poison." To the Nazi high command, it was also the perfect extermination weapon: the pesticide Zyklon B, as "experiments" in concentration camps showed, was capable of killing 1,492 prisoners in less than five minutes. And to the Old Queen in Snow White - who "made a poisoned comb, by arts which she understood" - it was almost invisible, undetectable, as a tool of murder.

What makes poison-murder stories so compelling, Bell posits, is the "betrayal of trust", where the victim takes the poison-laced substance from someone they know. The most extreme case of this, of course, is that of a parent - as in the case of Bell's grandfather - poisoning his or her own offspring. As Carl Jung wrote: "The Mother Archetype may connote anything secret, hidden, dark; the abyss, the world of the dead, anything that devours, seduces and poisons, that is terrifying and inescapable like fate."

Eventually, through tortuous detective work, Bell begins to pull the threads together. Macbeth, she discovers, was not her grandfather's real name: he'd taken it after seeing the play in Sydney and "knew the authority of a strong name". Nor was he originally American: his parents were first-generation Irish immigrants. His career was varied, and often criminal: during one stint posing as a psychiatrist he managed to defraud a patient of enough money to buy a car, employ a chauffeur and take up clay-pigeon shooting.

His reputation as a murderer - for which no court of law had ever found him guilty - she also reveals as anything but certain. His son Thomas, the "spastic", was in fact sent to a home, where he died aged 12. He was abandoned, forgotten; perhaps, in the end, as good as murdered. In the case of the other son, Patrick, Macbeth's guilt remains unproven.

Finally, her dossier assembled, Bell confronts her father, Macbeth's son. For a whole evening, the documents lie on his lap, unread. Eventually, and in his own time, he reads what his daughter has put together. And, in elaborate euphemisms, they discuss the family's "hardships". But, she writes, "we kept William out of the picture".

And yet he still haunts her: in a locked cabinet in her dining room she now has her own collection of poisons. "Is my collection an unconscious expression of some sort of attraction to power? Is this the slippery rock where my grandfather lost his footing?"