Guy's partner picked up by special agent (3)

I believe the answer is:

gal

I'm a little stuck... Click here to teach me more about this clue!

'guy's' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

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

Can you help me to learn more?

(Other definitions for gal that I've seen before include "Lady" , "Girl from American west" , "Broad" , "miss" , "Young woman (colloq.)" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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