I'm not sure I'd still recommend them now, but when I read them many, many years ago I really enjoyed David Morrell's [1] novels about highly trained assassins. They had titles of the form The $GROUP_OF_PEOPLE of the $THING: The Brotherhood of the Rose, The Fraternity of the Stone, The Covenant of the Flame, The League of Night and Fog (and maybe a few others whose titles didn't match that pattern, I think Testament was about the same characters, but can'lt really remember).

------------

[1] David Morrell is probably best known for First Blood, the novel Rambo is based on.