Set off in race to secure record (6)
I believe the answer is:
depart
'set off' is the definition.
(synonyms)
'race to secure record' is the wordplay.
'race' becomes 'dart' (darting is a kind of racing).
'to secure' indicates putting letters inside (inserted letters are secured inside).
'record' becomes 'EP' (abbreviation for extended play record).
'dart' enclosing 'ep' is 'DEPART'.
'in' acts as a link.
(Other definitions for depart that I've seen before include "Make an exit" , "Go away; deviate" , "21" , "Set out" , "Quit" .)