The film centers on George Arliss, who portrays the seemingly gentle village vicar, "Dr. Syn," in a quiet English community that finds itself under scrutiny from excise men searching for illegal goods coming from France. The audience is privy to the fact that he’s actually the clever criminal orchestrator of this carefully organized and profitable smuggling ring. The story follows his attempts to prevent the inquisitive "Capt. Collyer" (Roy Emerton) from uncovering the truth, as well as keeping “Imogene” (Margaret Lockwood) from discovering a more damaging secret. While Russell Thorndike’s novel was strong, the movie doesn't quite ignite with energy. It possesses an element of mystery, but neither Arliss nor the typically dependable Lockwood seem to be at their best. Roy William Neill, who later created the excellent Rathbone/Bruce “Sherlock Holmes” films, also seems out of sorts, resulting in a rather formulaic costume drama that should have been considerably more engaging – there are crypts, unsettling graveyards, and foggy marshes that could have been utilized to greater effect. I found it enjoyable enough, but my experience fell short of what I’d hoped for.

Source on TMDB