A Phone Call

Jeon Jungkook is a well known CBI officer. High ranks and most trusted officer in the whole Headquarters of SK. *Ring ring*
"Hello? Who is this?" He asked while pulling up his mobile to his ear to hear the answer of the individual on the phone.
"Your worst nightmare" the other person on the phone affirmed evilly and hung up.
Jungkook thought this phone call was a prank call because it was not abnormal for him to get these types of calls.

But the question arises........
Was this time really a prank call?
.........................