Endymion Porter conspired with Paul Pindar and Richard Boyle, the Earl of Cork, to remove Prime Minister Thomas Wentworth. To that end, they arranged for members of London's Trained Bands to confront King Charles and his wife Henrietta Maria as they rode by carriage from London to Oxford. Porter and his cohorts witnessed the events from Tyburn Hill, and saw the carriage accident which injured the king and killed his wife. This ensured Boyle's reign as Prime Minister.
Porter was sent to Westminster to have Captain Anthony Leebrick and his mercenaries, who had been employed by the King and Queen, sign a document stating that Thomas Wentworth was at fault for the incident. Porter was also to pay the group to leave England for Europe. However, Leebrick, knowing full well that he and his friends were in danger, quickly killed Porter by driving the quill that was to sign the statement into Endymion's left eye deep enough to pierce his brain.
The news of Porter's murder greatly shocked and disturbed Boyle as he considered him one of his closest friends. His death was cast as the final piece of fabricated, though incriminating, evidence against Wentworth.