Colonel Mustard?

I have done it.  Something I've always wanted to do.  Something I never really thought I would do.  Yes, ladies and gentlemen, I have signed up to go to a murder mystery mansion.  Perhaps the train murder mystery is more of the classic fantasy, but that cost twice as much.  I'll be going with my friend Katie in a few weeks, a perfect friend for such an adventure.  Katie and I are extreme kindred spirits and like randomly odd things in similar ways.  I will never forget the time when we were making our Peeps dioramas, and... Well, when a story begins with that sentence, do I even need to finish it?  The conundrum right now is: what to wear to the murderous affair?  The theme is "30s/40s gangster."  Can anyone think of a movie or send me a picture that will best exemplify this style?  We don't even technically have to dress up; the woman on the phone with the gravelly voice told me costumes are optional.  But if I'm driving an hour and a half to an eight acre estate (ALL TRUE), I best be dressed for the occasion.  What if it's just like Clue: The Movie?  One of my all time faves!  Admittedly, I'm nervous.  What if it's really creepy?  What if everyone there is weird (and not in the good way)?  What if there really is murder?  Maybe I should bring along a tommy gun just in case.  Now where did I put that thing?