Watches castle with boy following return of pipistrelles, perhaps (5,4,2)

'watches' is the definition.

'castle with boy following return of pipistrelles perhaps' is the wordplay.
I cannot quite understand how this works, but
'castle' could be 'keep' (I've seen this in other clues) and 'keep' is found within the answer.
'boy' could be 'tab' and 'tab' is found in the answer.
'of' could be 'o' and 'o' is found within the answer.
This explanation may well be incorrect...