Prisoner showing firm belief one working will be dropped (7)
I believe the answer is:
convict
'prisoner' is the definition.
(convict is a kind of prisoner)
'firm belief one working will be dropped' is the wordplay.
I cannot really see how this works, but
'firm' could be 'co' (a firm is a company) and 'co' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
This explanation may well be incorrect...
'showing' is the link.
Can you help me to learn more?
(Other definitions for convict that I've seen before include "One in prison" , "Prove guilty" , "Imprisoned criminal" , "Jailbird" , "Find or declare guilty" .)