On 20th June 1567, a few days after Scottish rebels apprehended Mary, Queen of Scots, servants of James Douglas, 4th Earl of Morton, allegedly found a silver casket of eight letters, two marriage contracts (which apparently proved that Mary had agreed to marry Bothwell before his divorce) and twelve sonnets. The casket was found in the possession of James Hepburn, 4th Earl of Bothwell and third husband of Mary, Queen of Scots.
What was important about these letters?
Well, the eight letters found in the casket were allegedly written by Mary to Bothwell and one was said to implicate the couple in the murder of Mary's second husband, Henry Stuart, Lord Darnley, in February 1567. Elizabeth I ordered a commission to investigate the matter of Mary's involvement in Darnley's murder and on the 14th December 1568 the letters were produced at the Royal Commission as proof against Mary.
In his excellent book on Mary Queen of Scots, My Heart is My Own, historian John Guy writes:
"The sole evidence that she was a part to the murder plot comes from them [the Casket Letters]. There is no other proof. Her guilt or innocence depends on whether the letters are true or false."1
