Jean Calas is sentenced to death on the wheel by the parlement of Toulouse. A Protestant Huguenot, Jean Calas has been convicted of murdering one of his sons after he told his parents of his plans to convert to Catholicism.
There's no real evidence to support the accusations, however, and it appears that Jean Calas is convicted and executed more out of fanatical anti-Protestantism among French Catholics than out of a pursuit of justice.
Voltaire is informed about the case after Calas is killed and uses it as part of a larger struggle to promote both religious tolerance in France as well as general legal reform. Voltaire has success, too, because Jean Calas will be exonerated in exactly three years.