who it is they’re meeting

(Grammar Questions I Couldn't Answer)

This question comes from Unit 2 Listening 1 of Q Skills 5.
A sentence in that listening read: 
Find out what kind of person is doing this kind of travel, what they’re doing when they get there, and just who it is they’re meeting. 

A student wondered whether "who it is they’re meeting" was a mistake.  Shouldn't it be "Who are they meeting?"

My initial response was to say that it was an indirect question.  But upon reflection, that didn't answer the question, because "Who are they meeting?" becomes "Find out who they are meeting".  Where was the "it is" in "who it is" coming from?