Joseph Cotten...
is a FINE actor, and I like his work very much in "Citizen Kane" and "Shadow of a Doubt".
He does seem, however, out of place in this film.
I understand that - in order to have the obligatory romantic happy ending where it is hinted that the lady will go off with the detective - the detective (much older and more of a father figure in the play and original movie), had to be made younger.
Although it was a supporting role in this film, I could have seen Cary Grant as the detective.