As a detective solving the mystery of the crossword clue ‘Knock on’, my thought process began by considering the various synonyms for ‘knock’. I considered phrases like ‘tap’, ‘pound’, ‘strike’, ‘rap’ and ‘beats’, all of which led me to the answer ‘RAPAT’. The key was recognizing that the word needed to fit into the structure of the crossword puzzle, with the final letters matching up with the intersecting words. The letters ‘R‘, ‘A‘, ‘P‘, ‘A‘, ‘T‘ provided the perfect fit, and with further investigation, I was able to confirm that ‘rap at‘ is indeed a common phrase used to describe knocking. This insight, combined with my detective skills, allowed me to confidently solve the crossword puzzle and reveal the answer to the mystery of the ‘Knock on‘ clue.