Stumble on the journey (4)
I believe the answer is:
trip
'stumble on the journey' is the definition.
(I've seen this before)
'stumble on the' is the wordplay.
'stumble' becomes 'rip' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'rip' put after 't' is 'TRIP'.
(Other definitions for trip that I've seen before include "Device working a trap or alarm when stumbled over" , "Tour; slip" , "Journey - miss one's footing" , "Outing; stumble" , "day out?" .)