Definition of "line of inquiry" []

• An ordering of questions so as to develop a particular argument (noun)

WordNet. Princeton University. 2010.

• "The reason why they had pursued this particular line of inquiry was because they had wondered if Randish's current mistress could lead them to a jealous husband or boyfriend lurking in the background, and it had obviously also occurred to Thanet that Elaine's employer could be the man they were seeking."