Going on (5)
I believe the answer is:
afoot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">going on</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for afoot that I've seen before include "In the wind" , "About to happen" , "Making progress" , "in preparation" , "Brewing" .)