On Good Friday 1882, 147 people in Inverness became severely ill after eating hot cross buns. While not fatal, they all experienced vomiting, tremors, and a dry throat. An unidentified alkaloid poison was found in the spice mix. The case was never solved.
To be honest though, hot cross buns do that at the best of times…
References
Dundee Courier. 11th April 1882. pg. 4
Inverness Courier. 13th June 1882. pg. 2