Plea of being elsewhere (5)
I believe the answer is:
alibi
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">plea of being elsewhere</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alibi that I've seen before include "Answer to charge - was somewhere else" , "Proof of not being at the scene of the crime" , "Timely excuse" , "Defence used by an accused person" , "Suspect's excuse" .)