There are two networks that make this story work. One of them is the group of individuals Smiley knows from his work during World War Two. It is because of this that Ailsa Brimley contacts him. She edits a small circulation Christian newspaper and has received a disturbing letter from a subscriber, Stella Rode who claims her husband, a teacher at the prestigous Carne public school, is going to kill her. She asks Smiley to take the letter to the local police after finding out that Stella has actually been killed.
The second network is that of the old boys at Carne and the staff and students of the school itself. This is a school for the highest echelons of the British ruling class, and le Carré wastes no time in letting the snobbery show itself. One of Carne's masters tells it like it is:
When I look back on my thirty years at Carne, I realise I have achieved rather less than a road sweeper... I used to regard a road sweeper as a person inferior to myself. Now, I rather doubt it. Something is dirty, he makes it clean, and the state of the world is advanced. But I-what have I done? Entrenched a ruling class which is distinguished by neither talent, culture, not wit; kept alive for one more generation the distinctions of a dead age.In order to solve the riddle, Smiley is the only one who can get into Carne. Not in a physical sense. But in a class sense. The local police know they can't find out what really happened because they're used to being met in the kitchen and offered a cup of tea. Smiley can meet the suspects on their own turf, in chapel, in their drawing rooms, at dinner parties and in the school itself.
Like all of le Carré's books this is tightly written. Descriptions are sparse, and tensions high. While the outcome of the detection is satisfying enough, the real story is the rigid prejudices of the British ruling class and their school system. For this reason alone while it is a novel first published in 1962 it has much to say about 2017.
le Carré - A Small Town in Germany