On the day of the Imnarja celebrations at the Grand Master's Palace in Valletta, a group of Muslim slaves planned to poison the banquet's food and launch attacks on auberges and other palaces. Some planned to assassinate Grand Master Manuel Pinto da Fonseca while others aimed to subdue the palace guards, liberate Muslim captives, and seize weapons from Fort Saint Elmo's armories. The Ottoman Beys had also prepared a fleet for invasion upon receiving a signal from the rebels.

The plot was discovered, and the knights acted quickly to quell the rebellion. This resulted in severe punishments, including execution and torture, for many of the enslaved individuals who were involved. The failed conspiracy was a pivotal moment in Malta's history, leading to increased oppression and control over the enslaved population.

One of the slaves implicated in the conspiracy had since embarked on the Order’s galleys, and did not know that the plot was foiled. One night, Our Lady of Trapani appeared to him and told him that one of his co-conspirators had betrayed him and that upon his return to Malta, he would be tortured and put to death. The slave asked the Virgin Lady for help, and she told him to seek out the ‘Jesuit of Floriana’. This Jesuit was none other than Padre Pierfrancesco Rossignoli, founder of the Manresa retreat house. Soon enough. the galley berthed in Malta and the slave was arrested, just as Our Lady of Trapani had told him. In prison, the slave asked for Rossignoli, who visited him frequently and baptised him. Even though he was still executed for his treason, the slave remained resolute in his faith in the Virgin of Trapani. His final words were ‘Giesu, Maria’. The slave’s serenity at the point of death led to a growth in the cult of Our Lady of Trapani amongst knights and the Maltese populace.