Go fishing but keep in touch (4,1,4)
I believe the answer is:
drop a line
'touch' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Maybe they are linked in a way I don't understand?
'go fishing but keep in' is the wordplay.
I cannot quite see how this works, but
'in' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for drop a line that I've seen is " Write".)