Behind That Curtain is the first non-silent movie to feature Charlie Chan. Actually "feature" is a strong word because Chan barely appears in it. He's mentioned early on as a great detective who occasionally helps the movie's main investigator and then he's brought in for the ending, but most of the film follows Scotland Yard detective Sir Frederick Bruce.
Even though Chan doesn't fit into it much, the plot is actually pretty cool. Or, it has the potential to be cool. Unrealized, but under different writers, it could've been really good.
A young heiress named Eve defies her controlling uncle and rejects her best friend in order to marry a louse named Eric Durand. As soon as they're hitched, Durand moves her to India and begins boinking the help. Then Eve gets word that Durand may have been involved in a murder back in England, so when Eve's jilted friend John, a world-traveling explorer, shows up in India, Eve leaves Durand and goes out into the desert with John. What adventures will they find? Will they find true love in each others arms? Is Durand really guilty of murder? It's up to Sir Frederick to find out.
Unfortunately, none of the answers are nearly as exciting as the questions. Eve and John don't really find adventure in the desert. Their time there is mostly spent lamenting their not being able to be lovers and John's trying to convince Eve to stay with him. True love eludes them though because Eve's a stupid decision-maker. Even the question of Durand's guilt is never seriously in doubt.
Behind That Curtain could've been a cool movie, with or without Charlie Chan, but instead it's a poorly executed, horribly acted mess. Lois Moran as Eve is especially bad. She delivers every line as melodramatically as possible, even for the '20s. E.L. Park is a goofy, charmless Charlie Chan too, so that when he finally shows up, you wonder what the point is.
Boris Karloff does show up in a bit part as John's manservant, but it's the only exciting part of an otherwise disappointing movie.