Investigation
This page is the CodyCross answer for the clue below from Department Store, Group 511, Puzzle 3 (Selfridges).
Question is: Investigation
and the answer is: RESEARCH
Word Meaning:
RESEARCH — (uncountable, countable in some dialects) Diligent inquiry or examination to seek or revise facts, principles, theories, applications, etc. (that are currently available, or that are familiar to one's self).
Definitions from Wiktionary.