No need to recap the plot. This is a badly flawed movie, despite "That Old Black Magic", though the magic clearly works for Monroe as she croons out the tune. It's clear that as an actress she's most comfortable with musical numbers, where her sparkle really gels.
The basic problem, as I see it, is with the script. There really isn't much story; as a result, something has to be added to hold audience interest besides budding super-star Marilyn. Apparently, colorful character was encouraged to pick up the slack. It looks like TCF found their answer in Murray's ear-splitting version of a Montana cowboy. I guess rural Montana doesn't have any grade schools where basic civility is taught. No need to belabor his maddening effect since others have made the same point at some length. Nonetheless, Murray's witless hollering of every line takes down the entire film. Nor does Monroe's squeaky southern accent that sort of comes and goes help. Nor is the over-extended final scene, where both actors revert to something more normal, enough to compensate for all the gaudiness that's gone before.
All in all, the movie's worth a 3, mainly for its excellent Technicolor staging, Monroe's singing, and the catchy title tune that was a chart-topper at the time. But beware the movie's moral, which seems to be a version of "All some people need in order to straighten out is a good beating"!
(In passing—Despite his misfire here, Murray was an excellent actor. Catch his carefully shaded performance in A Hatful of Rain (1957) or in The Bachelor Party (1957) to sample his true potential.)