Notebooks where one enters criminal riches (7)

'notebooks' is the definition.
(I've seen this in another clue)

'one enters criminal riches' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'enters' is an insertion indicator.
'criminal' indicates anagramming the letters.
'riches' with letters rearranged gives 'chiers'.
'a' going inside 'chiers' is 'CAHIERS'.

'where' acts as a link.