To remind you: that’s the encounter they talk about.

↓ Transcript
<Jester Book is sitting a bit away from the rest under some trees. Katharina is approaching him from behind>
Katharina: You knew her.
Book: <turns around> ... Miss Grauch?!
Katharina: The drak who attacked us in the tent. I was too scared to notice at the time ... but you knew each other. She was one of the guards in front of Lady Violet's mansion, wasn't she?
Book: She ... she was, yes. The one who insulted Master Peck, remember?
Katharina: I remember.
Book: Her name was Khima.
Katharina: <looks guilty> I ... didn't ask.
Katharina: ... but YOU! You told me you had no idea who the attackers were! You LIED to me!!
Book: I DIDN'T! Until I saw Khima I didn't recognize ANY of them! I DIDN'T KNOW the Lady was going to have us attacked! I swear!
Book: I ... I honestly thought she was trying to PLAY NICE this time. Still CALCULATED of course ... doing the Guild a favor so that Master Peck owes her one in the future ... and that she sent ME along to make sure everything goes smooth.
Book: <looks defeated> I ... REALLY thought she wouldn't do anything THIS despicable ...
Katharina: Oh COME ON!