plunge in | ˌplunge ˈinto sth
1.
to jump into sth, especially with force :
The pool was declared open and eager swimmers plunged in.
2.
to start doing sth in an enthusiastic way, especially without thinking carefully about what you are doing :
She was about to plunge into her story when the phone rang.
He's always plunging in at the deep end (= becoming involved in difficult situations without being well enough prepared) .