The word agent, so the dictionary says, ‘usually names the one who does the work as distinguished from the one who wills, plans, or orders’. It presumes a motive – be it an emotion or a desire, which operates on the will and definitely moves it to activity. In the mind of the lexicographer who merely seeks to discern and define the meanings of words, neither the meaning of agent nor that of motive is likely to trigger problematic or irksome associations. In covert human intelligence (HUMINT), however, things are different. ‘He’s an agent. He’s a man to be handled, not known’ is how a senior intelligence officer in John le Carré’s novel The Looking Glass War replies to a junior colleague’s inquiry about a man he has just been told ‘is not one of us’. When the junior officer goes on to suggest that loyalty must be behind the man’s readiness to act as an agent, he is told that ‘I mistrust reasons. I mistrust words like loyalty. And above all … I mistrust motive. We’re running an agent; the arithmetic is over.’