Wife has the plan to sharpen (4)
I believe the answer is:
whet
'sharpen' is the definition.
(whetting is a kind of sharpening)
'wife has the plan' is the wordplay.
'wife' becomes 'w' (abbreviation).
'has' is a charade indicator (letters next to each other).
'plan' indicates anagramming the letters (plan can mean organise).
'the' is an anagram of 'het'.
'w'+'het'='WHET'
'to' is the link.
(Other definitions for whet that I've seen before include "grind" , "Sharpen by grinding" , "Sharpen - stimulate" , "Sharpen, appetite or razor" , "'Sharpen, appetite say (4)'" .)