Where we all leave service book (4,6)

I believe the answer is:

mass exodus

'where we all leave' is the definition.
(the process of lots of people leaving somewhere)

'service book' is the wordplay.
'service' becomes 'mass' (I've seen this in other clues).
'book' becomes 'exodus' (I've seen this before).
'mass'+'exodus'='MASS EXODUS'

I've seen this clue in The Guardian.

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