I’d like to suggest that you NOT read plot summaries before you go.
Good movies rely on a number of audience reactions, and knowing the plot in advance sort of ruins the movie’s ability to cause reactions. Plus, movies often depend on atmosphere, on lighting, or cutting, or various aspects that have little to do with “plot.” Example: “there’s a car chase” would describe the plots of lots of movies, but some car chases are very exciting and some are quite humdrum.
How would a plot summary of a Marx Brothers’ movie be helpful? What would it say that was even remotely relevant?
If you want to get a one or two sentence idea of what a movie is about, IMDB is just fine, it seems to me. For the MALTESE FALCON, if you really want more details, you could get a fairly good plot summary by reading, um, lessee, oh, I dunno, try a book by Dashiell Hammett, that could be pretty helpful.