Though more often used in social contexts than spy groups, you may be thinking of clique.

clique: A small, exclusive group of individuals; cabal

cabal and coterie are both listed as synonyms. You could also use circle.

Though if you're focusing more on the shared-philosophy aspect than the distinct-group aspect, there's

camp: A group of people with the same strong ideals or political leanings.

or even cult.

Though more often used in social contexts than spy groups, you may be thinking of clique. it starts with a "c" and has a negative connotation.

clique: A small, exclusive group of individuals; cabal

cabal and coterie are both listed as synonyms. You could also use circle.

Though if you're focusing more on the shared-philosophy aspect than the distinct-group aspect, there's

camp: A group of people with the same strong ideals or political leanings.

comrades, or even cult.

Though more often used in social contexts than spy groups, you may be thinking of clique.

clique: A small, exclusive group of individuals; cabal

Though more often used in social contexts than spy groups, you may be thinking of clique.

clique: A small, exclusive group of individuals; cabal

cabal and coterie are both listed as synonyms. You could also use circle.

Though if you're focusing more on the shared-philosophy aspect than the distinct-group aspect, there's

camp: A group of people with the same strong ideals or political leanings.

or even cult.