Had crept off, or walked off with (6)
I believe the answer is:
stolen
'had crept off' is the definition.
I can't judge whether this definition defines the answer.
'walked off with' is the wordplay.
'walked' becomes 'stole' (stealing is a kind of walking).
'off with' becomes 'n' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'stole'+'n'='STOLEN'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for stolen that I've seen before include "Robbed" , "Taken without right" , "Purloined in Solent" , "` `The ... Child' ' (Yeats)" , "Pilfered" .)