I think the mystery caller is either that lady who snuck out just before main girl got a call, or the whole thing is just a ploy by boss to make the employees hookup.
Who could have known in the agence that MC is going back to his hometown ?
If mc, fmc didn't tell anyone, then it has to be from the Father who certainly said it to the rest of the family.
Meaning someone in the agence has a link to mc's familiy ?
Do we have a losing childhood friend heroine ?
@Greyhood we saw early the MC's mum works in the jtc branch in her area and she was told by a co-worker that knew through a gossip network so it was probably spread some what organically since people train together and get transfered but keep in touch