Capture spies allegedly (5)
I believe the answer is:
seize
'capture' is the definition.
(synonyms)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for seize that I've seen before include "Take by force" , "Suddenly take hold of" , "Get hold of" , "Confiscate" , "Grab suddenly" .)