be in on   (TTS發音)

be party to； be fully involved in參與；完全卷入

    He is in on the whole sordid business. 他參與了整個這場骯髒的勾當。

    They were de finitely in on the consiracy. 他們肯定完全參與了這一陰謀。

    I'm sure she's in on their plans. 我肯定她跟他們同謀。