on the insideidiom
Definition of on the inside
1 : on the inner side, edge, or surface of something The number 22 car tried to pass the leader on the inside (of the track).
2 baseball : on the side of home plate nearest the batter The next pitch was a fastball on the inside.
3 —used to describe how someone is feeling She may have seemed happy, but really she was sad on the inside.
4 : in a position within an organization or group : working for an organization The bank robbers must have had help from someone on the inside.
5 : in prison He wondered what life was like on the inside.