Callan was an assassin, a born killer who worked for a 'government department.' This was the sort of government department that took care of undesirables and did all the dirty jobs that the government could not be seen to be involved in. Most people in the government would probably be horrified if they knew it existed !! He was aided by a petty crook called Lonely, wonderfully played by Russel Hunter. Lonely was afraid of Callan but respected him above all else. Along with Cross and Meres, Callan worked for a man called Hunter played by various actors. The stories were good, very dark and rather believable. I don't know if departments like this exist .... maybe, maybe not. 9/10
