The term 'plunge into' can be broken down into three words: DIP (3 letters), DELVE (5 letters), and IMMERSE (7 letters). To 'DIP' is to quickly put something into a liquid or other substance and then take it out again. To 'DELVE' is to investigate or look deeply into something, often for a long period of time. To 'IMMERSE' is to become deeply involved in something, often to the point of forgetting everything else. Therefore, the phrase 'plunge into' can be interpreted as quickly entering into something, investigating it deeply, and becoming completely absorbed in it.