On a Saturday in the little town of Leongatha in Victoria's east, a group gathered for lunch at a home nestled in the trees.
Four people shared a meal — now, three are dead and the other is fighting for his life.
Detectives have not laid any charges, but say the woman who cooked the meal, 48-year-old Erin Patterson, remains a suspect.
Here's what we know so far.
Police say a group gathered for lunch at Erin Patterson's Leongatha home on Saturday, July 29.
In attendance were Ms Patterson, two children, and two married couples: Heather and Ian Wilkinson, and Gail and Don Patterson.
Gail Patterson was the sister of Ms Wilkinson, and the mother-in-law of Erin. Erin is separated from her ex-husband, and police said their relationship was amicable.
After leaving the lunch, the Wilkinsons and Pattersons began developing what felt like food poisoning over the course of that night and the next morning.
They went to local hospitals in Leongatha and Korumburra, before being taken to the Austin Hospital in Melbourne's north-east.
Ms Wilkinson and Ms Patterson died on Friday, August 4, and Mr Patterson died the next day. Mr Wilkinson remains in hospital in a critical condition.
Police say they displayed symptoms of having consumed the highly poisonous death cap mushroom, which is responsible for nine out of 10 mushroom deaths globally.