Tour could be mistake (4)
I believe the answer is:
trip
I believe this clue is a double definition.
'tour' is the first definition.
(I know that journey is a is a more specific form of the action of tour)
'be mistake' is the second definition.
(I've seen this before)
'could' is the link.
(Other definitions for trip that I've seen before include "Jaunt" , "Hallucinogenic drug experience - lose one's balance" , "Stumble - excursion" , "Journey, excursion" , "Set off for" .)