plunge in/plunge into something
phrasal verb with plunge verb uk/plʌndʒ/ us/plʌndʒ/
C2 突然开始积极地做
to suddenly start doing something actively or enthusiastically
Two months before his exams, he suddenly plunged into his studies. 考试前的两个月，他突然开始埋头学习。
He took a deep breath and plunged into his speech. 他深吸了一口气，开始热情洋溢地讲了起来。