Person seeking forgiveness in prison, one figure locked up (8)
I believe the answer is:
penitent
'person seeking forgiveness' is the definition.
'in prison one figure locked up' is the wordplay.
'in prison' becomes 'pent' ('pent' can mean 'confined').
'one' becomes 'i' (Roman numeral).
'figure' becomes 'ten' (I've seen this in other clues**).
'locked up' indicates putting letters inside.
'i'+'ten'='iten'
'pent' placed around 'iten' is 'PENITENT'.
(Other definitions for penitent that I've seen before include "Repentant" , "Rueful" , "I'm sorry" , "Expressing sorrow for one's sins" , "Conscience-stricken" .)