The Problem in Spying (Mycroft Holmes/Original Male Character)

Robert is a military man in every sense of the word, also a member of the British royal family and a former member of MI5.
Mycroft Holmes is a former lieutenant in the Coldstream Guards with a background in MI6 and later became the British government himself.
The problem comes when the British government and both MI5 & MI6 enter into an argument that separates the two allied forces.
Both forces send their best man to spy on the other
What could possibly go wrong