There are lots of references to James Bond and although the point is made that in real life spying is nowhere near as glamorous or interesting the threat of death is real.
The two men believed to have the makings of a double agent are Castle and his colleague and it is Davis that the authorities make their target. He has the tip-off from Castle that a leak has probably happened and they are trying to turn the pressure up but he seems to take it all as a joke.
In parallel the pressure is also being put on Castle, who constantly dreams of retirement, with the ghosts of his past in South Africa coming back to haunt him in his own home.
The upshot of it is that at the top of the tree those running the department have a complete disconnect with those they are in charge of giving rise to both humour and tragedy.