 In the Hercule Poirot novel "The Clocks", the pseudonymous secret agent Colin Lamb is heavily implied to be the son of the now-retired Battle.Battle also has a secret professional life that is revealed in the denouement to "The Seven Dials Mystery", but this is never referred to again.In this novel he states, that 
"half the people who spent their lives avoiding being run over buses had much better be run over and put safely out of the way.