Scheduled to work outside at night with 〜ことになっている

Grammar Explanation: Past decision still in effect with 〜ことになっている

Kate says she wants to study together with Emiriko before bedtime.

エミリコ:: 「あっ…　ごめんなさい。実(じつ)は外(そと)の仕事(しごと)を深夜(しんや)にもすることになって…」; “Ah, I'm sorry. The truth is, I'm scheduled to do late-night work outside...”; 「また別(べつ)の機会(きかい)にお願(ねが)いします！」; “Please ask again another time!”

Key Points

することになって points to an assigned plan
- 外(そと)の仕事(しごと)を深夜(しんや)にもすることになって means Emiriko has been scheduled to work outside late at night too.
- The sentence trails off because this explains why she cannot study now.
実は introduces the real reason
- 実(じつ)は signals that she is revealing the actual scheduling conflict.
- It softens the refusal before she apologizes.
また別の機会に politely postpones
- また別(べつ)の機会(きかい)に means “another time”.
- お願いします keeps the refusal deferential toward Kate.