England ? It’s a culinary mystery worthy of Agatha Christie.

Britain’s Health Protection Agency said Friday about 400 people reported falling ill after eating at The Fat Duck, a world-renowned British establishment famed for dishes such as snail porridge and bacon-and-egg ice cream. Health officials are baffled by the outbreak of diarrhea and vomiting while the celebrity chef, Heston Blumenthal, has said his restaurant will remain closed until the mystery is solved.

“It’s so weird — we haven’t found anything. But I can’t take the risk of keeping open until we have exhausted every single avenue,” Blumenthal told The Times of London last week, shortly after the first group of people reported falling ill.