Without walls round US prison, spy finally escaping (4-4)
I believe the answer is:
open-plan
'without walls' is the definition.
(I've seen this before)
'round us prison spy finally escaping' is the wordplay.
I cannot really understand how this works, but
'round' could be 'o' (round can mean a round object) and 'o' is found within the answer.
'prison' could be 'pen' (I've seen this in another clue) and 'pen' is found in the answer.
The remaining letters 'plan' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for open-plan that I've seen before include "Without internal walls" , "Office without walls" , "Having no internal partitions" , "No pen pal in office lay-out without partitions" , "Having no walls between areas" .)