The museum was recently 'plunged into' scandal when it was learned that some of its art had been sold on the black market.
We've been thinking of buying a new car, and yesterday we finally 'took the plunge'. [=we bought a new car]
A series of bad management decisions are responsible for the company's 'plunge into' debt.
(..) whether you believe them or not." How? MESSINGER: You choose. SETH: Choose? To fall to Earth. You take the plunge, the tumble, the dive. You jump off a bridge. Leap out a window. You just make up your mind to do it and you do it. (..)1998 City of Angels