barking up the wrong tree
US /ˈbɑːrkɪŋ ʌp ðə rɔŋ triː/
UK /ˈbɑːrkɪŋ ʌp ðə rɔŋ triː/
1.
to be pursuing a mistaken course of action or to have a wrong idea about something
:
•
If you think I stole your pen, you're barking up the wrong tree; I haven't seen it.
•
The police were barking up the wrong tree when they suspected the innocent man.