Follow part of castle path (4,5)
I believe the answer is:
keep track
'follow' is the definition.
(follow can mean to keep track of something)
'part of castle path' is the wordplay.
'part of castle' becomes 'keep' (keep is a part of a castle).
'path' becomes 'track' (track is a kind of path).
'keep'+'track'='KEEP TRACK'
(Other definitions for keep track that I've seen before include "Stay in touch, be informed about" , "Remain in touch or informed about" .)