Caroline Grills (née Mickelson) was born between 1888 and 1890 in Balmain, New South Wales, Australia. She married Richard William Grills on April 22, 1908, and together they had four sons. Known for her sociable nature, Caroline often hosted family gatherings, during which she would serve tea, cakes, and biscuits. Her outwardly caring demeanor earned her the affectionate nickname "Aunt Carrie" among her relatives.

Between 1947 and 1953, Caroline Grills embarked on a series of poisonings that led to the deaths of several family members. Her modus operandi involved administering thallium, a common rat poison at the time, to her victims through food and beverages. The victims exhibited symptoms such as hair loss, nervous disorders, and blindness before succumbing to the poison.

Her first suspected victim was her 87-year-old stepmother, Christine Mickelson, who died in 1947. This was followed by the deaths of relatives Angelina Thomas and John Lundberg. In 1948, her sister-in-law, Mary Anne Mickelson, fell ill with similar symptoms and died on February 15, 1949. Despite the pattern of mysterious illnesses and deaths within the family, suspicions were not immediately raised.

The turning point came in 1953 when Christine and John Downey of Redfern, both of whom had been served tea by Caroline, fell ill. Authorities tested the tea and discovered it contained thallium. This led to Caroline's arrest and subsequent trial. On October 15, 1953, she was convicted of the attempted murder of Eveline Lundberg and sentenced to death, a sentence later commuted to life imprisonment. While she was only convicted for one attempted murder, she was suspected in the deaths of at least four family members.​

During her time at Sydney's Long Bay Prison, fellow inmates dubbed her "Aunt Thally," a grim nod to her method of poisoning. Caroline Grills died on October 6, 1960, from peritonitis caused by a ruptured gastric ulcer. Her case remains one of Australia's most notorious instances of familial serial killings.​