Let in to confess (5)
I believe the answer is:
admit
I believe this clue is a double definition.
'let in' is the first definition.
(synonyms)
'confess' is the second definition.
(I've seen this before)
'to' is the link.
(Other definitions for admit that I've seen before include "Disclose" , "Confess - let in" , "Allow to enter; own up" , "Allow entry" , "Stop being obstructive" .)