Some intercepted letters sent to the French ambassador Michel de Castelnau showed that he wished to serve Elizabeth I.
[5] In July 1592 the English ambassador Robert Bowes reported that Mowbray had brought letters to Scotland from Spain.
Bowes recommended Mowbray to William Cecil as someone who could do some service for England as he was sent abroad on the affairs of Catholics, but he wanted more money than he had previously received.
[6] On 14 April 1596 he wounded William Schaw, the royal master of work, with a rapier, apparently in a family feud.
[11] On 5 October it was agreed that Mowbray and his servant George Brock would go to Rossend Castle in the custody of Sir Robert Melville and then leave Scotland.
[13] Mowbray wrote to Cecil from Edinburgh complaining about the Scottish merchant and poet John Burrell in London who ridiculed him in verse and now had a sonnet against him published.
[14] In October 1602, in England, an Italian called Daniel Archdeacon accused him of treason against James VI of Scotland.
[19] A French diplomat, the Baron de Tour interviewed Archdeacon, and found him to be both "a witty man and a cunning corrupted person."
De Tour took the idea of plot seriously, and advised James VI that Mowbray should be tortured, rather than fight a duel with the Italian.
Mowbray explained his disappointment that his nephew's ward and marriage had passed from William Schaw to Laird of Easter Wemyss, but claimed not to have spoken against the king because of it, or to have criticised James VI for his reaction to the execution of Mary, Queen of Scots.
Archdeacon had told them he had used a metaphor of sarks (shirts), coats, and skins about the king and his mother, which Mowbray denied.