Governess keeps one in mountain retreat (5)
I believe the answer is:
eyrie
'mountain retreat' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'governess keeps one' is the wordplay.
'governess' becomes 'eyre' (Jane Eyre is a governess in the novel Jane Eyre).
'keeps' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'eyre' enclosing 'i' is 'EYRIE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for eyrie that I've seen before include "cliff top home" , "elevated position" , "An eagle's nest (5)" , "Nest of 19 Across" , "Eagle's lair" .)