I wouldn't have expected to see Gary Cooper in a romantic comedy. The few Westerns with him I've seen, he never seemed to have much chemistry with his female co-stars. He always seemed stiff too me. Which I don't think vanished when I watched Casanova Brown, but maybe it works it uses that to its advantage.
Cooper is a literature professor, all set to marry Madge Ferris in the small town of Rossmere, IL, despite his future father-in-law (Frank Morgan playing a loudmouth curmudgeon) advising him against marriage. The day of the rehearsal, Brown receives a letter from a maternity hospital in Chicago, requesting he come quickly, though the letter doesn't explain why. Brown reveals that a year or so earlier, when he traveled to New York to research a book he was writing on his ancestor, the famous Casanova. While there, he met Isabel (Teresa Wright), and they fell in love and got married.
Then he met her family, and her mother, in addition to hating smokers and liars (and especially people who lie about about smoking), believes in astrology. Going by when they were married, and when he was born, she proclaims the marriage catastrophic. Brown tries to remain polite, but finally loses his temper and unloads his feelings on astrological hokum. His point is somewhat undercut when the cigarette he tried to snuff out in his handkerchief lights it on fire. Then it lights his coat on fire, which lights the couch on fire. Meanwhile, the cigarette had been thrown in the trash can, and has started a fire there. Rather than letting it burn itself out, the idiots tell their butler to try and take the can outside, and he trips, starting a fire in their library. And the whole house burns down.
The marriage is annulled shortly thereafter.
Cass can't figure why he would need to go to Chicago, given all that took place in New York, but he goes, and learns Isabel had a girl, and she's planning to put the baby up for adoption. Cass, naturally, throws on some scrubs and steals the baby, setting up shop in a hotel room, where a maid and the doorman help him care for the baby. Meanwhile, Madge is trying to figure out what's going on, we learn Isabel never intended to give the baby up, but was only using the hospital as a way to get Cass there, Cass is convinced he has no parental rights and tries to convince the maid to marry him so he doesn't lose the child.
I recognize this is set in the 1940s, and that even today, courts tend to side with the mother when it comes to custody. But surely, if one parent wants to care for the child, while the other doesn't, that would be allowed, barring some definitive proof they were unfit? Admittedly, Cass is now guilty of kidnapping (his kid or not, I'm pretty sure you can't just yoink a kid from a hospital nursery). That aside, he seems a diligent, if somewhat overprotective, dutifully employed parent. It seems odd that the courts would actually say, "nope, go ahead and adopt the kid out". But the courts are a mess, and even if they wouldn't, I guess there's no reason Cass would know that.
The romantic aspects of the movie don't really work. We don't see Cass interact enough with Madge or Isabel to feel a real connection between either pairing. Cass/Isabel gets more time, but they spend a lot of it arguing, and given Cass' experiences at the maternity hospital (he gets the runaround from a bunch of nurses, then a bunch of procedures, and no one will explain what any of it is for until it's over), which he's put through because of her, it's hard for me to like her much. I don't think Cooper has great comic timing or anything, but I think he does alright playing a guy who's kind of befuddled by people. He takes the stiffness I see in him, and makes it into a sort of awkwardness, the well-meaning fool.
It's not a great movie, but it was worthwhile for me to see Cooper in a different role.