turnkey
noun
definition* : one who has control of the keys in a prison or jail; jailer.
adjective
definition: of or relating to a building, system, or the like, that is sold, supplied, or installed complete and ready to occupy or operate.
example: He bought a turnkey restaurant which had once been a successful business.
Quotation:
* “This turnkey had given him to understand that he was lodged, like some few others in the jail, apart from the mass of prisoners; because he was not supposed to be utterly depraved and irreclaimable, and had never occupied apartments in that mansion before.” (Charles Dickens, Little Dorrit )