 He is sent to Portugal to monitor the Duke and Duchess of Windsor; when they move to the Bahamas, Mountstuart follows, playing golf with the Duke and socialising regularly until the murder of Sir Harry Oakes.Mountstuart suspects the Duke is a conspirator after two hired detectives ask him to incriminate Oakes' son-in-law with false fingerprint evidence.Mountstuart refuses and is called a "Judas" by the Duchess.