The accidental assassin - Jan Toms

Victor Green is 37, unmarried and the sort of man who irons his underpants. When pruning his tree, he falls from his ladder and kills the pedestrian below - the gangster Tommy 'Gruesome' Hewson. As word spreads of the gangster's demise, Victor is mistaken for Vincent Green, an international hitman, and swept into a turf war between two local gangs.
The hapless Victor's life is turned upside down as he inherits Tommy's poodle, gets a girlfriend and is recruited to fight in both gangs, accidentally leaving a trail of bodies in his wake as he tries to figure out what seems to be a horrific misunderstanding.