Plea of being elsewhere (5)
I believe the answer is:
alibi
'plea of being elsewhere' is the definition.
(I've seen this before)
This is all the clue.
(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" .)