Australian police have launched an investigation after three people died and a fourth was left needing a liver transplant after eating what authorities suspect were death cap mushrooms.

Australia is gripped by the mysterious deaths of three people in a suspected poisoning case that reads like a fictional thriller.

Two couples were invited to lunch at a palatial country home in the state of Victoria one Saturday in late July. They included a local pastor and his wife. All four were known to locals as pillars of the tightknit rural community.

That night, they all became seriously ill with what appeared to be food poisoning. A week later, three of the four were dead. One man remains in hospital in a critical condition, awaiting a liver transplant. The host of the gathering — a woman in her 40s — and her two children were unharmed.

Police suspect the victims ate death cap, or Amanita phalloides, mushrooms, one of the deadliest known mushrooms to humans. But whether the poisonings were intentional, or if the fungus is even the culprit, is shrouded in mystery. The guests’ symptoms were consistent with mushroom poisoning, medical experts and investigators say.

Homicide detectives have searched the home of Erin Patterson, the 48-year-old woman who hosted the gathering in Leongatha, about 70 miles southeast of Melbourne. She was taken in for questioning Saturday and released without charge later that evening.

During the search, investigators seized several items they say are of interest to the case. A food dehydrator found at a local landfill is apparently also being tested to see if there is any link, Melbourne’s Age newspaper reported, citing an anonymous police source close to the investigation. Police declined to confirm whether a dehydrator is among the items being examined.