Southampton Plot

Edmund Mortimer, 5th Earl of March, was the great-grandson of Lionel of Antwerp, Duke of Clarence, second surviving son of King Edward III, and his claim to the throne was thus superior, should one allow female intermediaries (he was the grandson of Philippa of Clarence, daughter of Lionel), to that of Henry V and his father, Henry IV, who derived their claim from Henry IV's father, John of Gaunt, third surviving son of Edward III.

[1] The three ringleaders of the plot were Edmund Mortimer's brother-in-law, Richard of Conisburgh, 3rd Earl of Cambridge (also grandson of Edward III through his fourth surviving son, Edmund of Langley, and thus also Mortimer's first cousin twice removed); Henry Scrope, 3rd Baron Scrope of Masham (whose uncle Richard le Scrope had been executed for his part in a 1405 revolt); and Sir Thomas Grey, whose son, Thomas, had been betrothed in 1412 to Cambridge's only daughter, Isabel.

[2] The nominal principal, the Earl of March, informed King Henry of the plot on 31 July, stating that he had only just become aware of it.

[5] Pugh also contends that "there was no plot in 1415 to assassinate Henry V and his three brothers and that heinous charge, by far the most sensational in the indictment, was fabricated to ensure that Cambridge, Grey and Scrope did not escape the death penalty as a well-deserved punishment for the various other offences that they undoubtedly had committed".

It is also portrayed in the anonymous play, The History of Sir John Oldcastle (c.1600) and in William Kenrick's Falstaff's Wedding (1760).