It's a Wonderful World (1939)
A comedy with the creds to guarantee a decent success-James Stewart and Claudette Colbert as leads, a script written and screenwritten by Ben Hecht, and direction by the solid W. S. Van Dyke. So it clicks quickly into play with a serious seeming plot (independent detectives and a crime) in a chipper entertaining tone (fast and easy). There is a clear lack of depth as you go-this isn't going to be a moving or hard hitting classic, but rather a fun and well crafted entertainment-and it's too bad. The basics are here to make a really fine movie.
And that's what keeps it going-the really fine movie part. There is first of all a sincere performance by Stewart, earnest and nuanced as the regular guy detective who knows good from bad (an important distinction here). He goes quickly out on a limb and he cuts through the sometimes corny side characters. Colbert, when she shows up, is no Myrna Loy (Van Dyke directed the first "Thin Man"), but I like her a lot (she was in "It Happened One Night") and she gives the comedy a zaniness that works.
But Stewart never cracks a smile, and it's a relief because he's the backbone of an improbable series of events. The murder itself is practically the McGuffin here-the screwball romance part of things is the main plot. What matters more is Stewart and Colbert-picking apples as enemies, for example. They both need the food, and both don't trust the other, but they are both nice people at heart and so it kind of happens to make sense in a funny way.