Mary Blandy was led astray by a lover who, although already involved in a common-law marriage, was eager to obtain the dowry of £10,000 which her father had unwisely advertised he would give her.  This lover, Cranstoun, sent her arsenic, which she gave her father over the course of months.  Blandy never denied having administered the poison, but she did insist throughout her trial and until her death that she had believed that the powder she stirred into her father's tea and gruel was merely an unknown substance that would improve his opinion of Mr. Cranstoun.  The jury didn't believe her.