Who are the men in black who selflessly put themselves in the line of fire? In Rules of Engagement, the first episode of the three part documentary series Line of Fire, we get our first glimpse behind the balaclava and delve into the covert and controversial world that is the Armed Offenders Squad (AOS). Discover the genesis of this elite squad in the 1960s, the vital lessons learnt the hard way, and explore the conflicting reactions to the first fatal shootings in the 1970s.