@cleverjake, M.O. = modus operandi = 'way of working', i.e. how they did it. You answered why, I think. Then I read on to 'indiscriminatory' and gave up on the whole thing. ;)
For fiction, I'd vote for the First and Second Chronicles of Thomas Covenant by Stephen Donaldson.
He's often mocked for deploying the less-visited corners of the OED, but some people love that sort of joy in language. The antihero has never been done better, and the inversion of the whole 'wake up in a fantasy land' trope is brilliant and explored to its logical conclusions.
Give it to Book 2 of the First Chronicles ('The Illearth War') before you decide whether you like them.