It didn't take long for us to find out what happened to Hye In. She had gone missing towards the end of ep 4. She played a key role in the rescue mission of the president's daughter.
Perhaps the daughter will appear in future episodes but I was a bit surprised to see her disappear after being rescued. I thought she would stick around a bit longer.
With Hye In now at NTS, you assume that Son Hyuk will continuously use her to get info that he can't get himself. No one seems happier to have Hye In at NTS than Jung Woo. It'll be interesting to see what develops with Jung Woo, Hye In and Son Hyuk in the same building. The NTS agents don't want DIS around so I doubt they'll work together well.
On a side note, the last few episodes have helped in clearing quite a bit of what's going on.