Fictional detective Sam, seen originally in a suit (6)
I believe the answer is:
spades
'suit' is the definition.
(I've seen this before)
'fictional detective sam' is the wordplay.
'fictional detective' becomes 'spade' (I've seen this before).
'sam' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'spade'+'s'='SPADES'
'seen originally in a' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for spades that I've seen before include "dark suit" , "Black suit" , "They may turn up" , "Passed around with diggers" , "Suit in pack of cards" .)