Tube line inspector finishes article probing Vikings' fates (8)
I believe the answer is:
northern
'tube line' is the definition.
'northern' can be an answer for 'line' (I have seen 'Black line' mean 'northern' so perhaps 'line' could also mean 'northern'). I'm not sure about the 'tube' bit.
'inspector finishes article probing vikings' fates' is the wordplay.
'finishes' says to take the final letters (I've seen 'finish of' mean this).
'article' becomes 'the' (the definite article in English).
'probing' is an insertion indicator (probe can mean to make a hole in).
'vikings' fates' becomes 'norn' (I am not sure about this - if you are sure you should believe this answer much more).
The last letter of 'inspector' is 'r'.
'r'+'the'='rthe'
'rthe' placed inside 'norn' is 'NORTHERN'.
Can you help me to learn more?
(Other definitions for northern that I've seen before include "Upwards, as seen in charts" , "Arctic - polar" , "Sky phenomenon" , "Of the direction of a compass needle" , "Coming from boreal parts" .)