Viking raid — no help is secured by hooter (5)
I believe the answer is:
norse
'viking' is the definition.
(the Vikings were a Norse people)
'help is secured by hooter' is the wordplay.
'help' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'is secured by' means one lot of letters goes inside another (inserted letters are held or secured).
'hooter' becomes 'nose' (I've seen this before).
'r' placed within 'nose' is 'NORSE'.
'raid no' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for norse that I've seen before include "Relating to ancient Scandinavia" , "Old form of Norwegian" , "Old Scandinavian language" , "Of old Scandinavia" , "Relating to Norway" .)