Cardinal Alfonso Petrucci was strangled in his cell in the Castel Sant'Angelo, Rome on 4 July 1517. He was 26. He had been a prisoner in the papal fortress for six weeks, one of five cardinals accused of plotting to poison Pope Leo X. His execution was judicially sanctioned, but in the most dubious of circumstances. Right from the start, observers asked whether there was really a plot, or whether Petrucci and his colleagues were framed by Leo in his pursuit of power, wealth and the interests of his family, the Medici. The ‘abominable case' of the Cardinals' Conspiracy is one of the great Renaissance mysteries.