Secret Service? (9)

I believe the answer is:

underhand

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'secret' is the definition.
(underhand means secret or duplicitous)

I can't explain the rest of the clue.

(Other definitions for underhand that I've seen before include "done deviously through cover" , "Surreptitiously, sounds like a lower employee" , "delivery may be so made" , "Deceptively" , "Displaying craft" .)

I've seen this clue in The Telegraph.

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