Involve and take the plunge! (7)

I believe the answer is:

immerse

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'the plunge' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for immerse that I've seen before include "Plunge, dip, submerge" , "Dip under the surface of a liquid completely" , "Drown" , "duck" , "Baptise" .)

I've seen this clue in the Evening Standard.

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