"The Mysterious Mr. Wong" opens with expository information from an encyclopedia about the fabled twelve coins of Confucius and how the person who possesses them will rule a province called Keelat. Afterwards, newspaper story about a murder appears. Indeed, newspaper accounts of homicides in Chinatown recur throughout the narrative. Three slayings occur in rapid succession during the first few minutes. The police believe that the Tongs are on the warpath. The first victim staggers out into a street and collapses. A man searches his body, finds a perforated coin, and plants a note with a Chinese letter on the corpse. The second victim has been hanged, and hands rifle his pockets to acquire a coin. The third man is strangled as he sleeps—yes, he is strangled perhaps too quickly, but the Production Code censors might have forced Nigh to accelerate this lurid death scene—and hands plunder his warm corpse, extract the coin from a shoe, and leave the usual note on his body. Meanwhile, agents of the Keelat province show up in town to thwart Mr. Wong. Phillip Tsang (E. Alyn Warren of "Chinatown Squad") heads up the operation. Eventually, Tsang crosses paths with Mr. Wong, and Wong takes him hostage.
A cynical newspaper reporter, Jason Barton (Wallace Ford of "Freaks"), investigates these murders. The authorities are convinced that the Tongs are responsible. Barton disagrees in a news story, and his editor Steve Brandon (Lee Shumway of "The Lone Star Ranger"), packs him off to find a Chinaman named Wong. "Did you ever run into a Chinaman by the name of Wong?" Brandon inquires. "Have I ever run into any that ain't named Wong?" Barton retorts. Our journalistic hero ventures into Sam Toy's Laundry where he encounters an Irish cop, Officer 'Mac' McGillicuddy (Robert Emmett 0'Conner of "Picture Snatcher"), who seems to be the only policeman walking a beat in the district. He shares Barton's racism and refers to the Chinese as "monkeys." None of the other reporters are interested in the murder. Barton checks over the body and learns that Toy died with a pencil in his hand. A breeze blows through the laundry when Mac opens the door and Barton finds a message written in Chinese. He visits the herb shop of Mr. Lysee (Bela Lugosi), but Lysee plays dumb when Barton quizzes him. Barton visits a nearby university where Professor Chan Fu (Luke Chan) works as a translator. Lysee sends one of his minions to steal the note from Barton, but Barton eludes him.
Later, Barton ransacks Toy's laundry and finds the last coin, but an assailant gets the drop on Barton and steals the last coin. When Barton recovers, he learns another Chinaman has died. "Say, this is getting monotonous," Barton complains, "I'm supposed to bring in real live news, the best I can do is run down dead Chinamen." Later, Barton and the newspaper switchboard operator, Peg (Arlene Judge of "Flying Devils"), have dinner in a restaurant and Barton discovers that the man who stole the coin from him is trying to return it. This man dies in the booth next to Barton and Peg. Afterward, Mr. Wong's murderous minions capture Barton and Peg. Eventually, Wong takes them to his underground torture chamber where he plans to stick bamboo shafts up Peg's finger nails unless the reticent Barton surrenders the last coin.
Just before the torture commences, Wong and company leave our hero and heroine alone long enough for Barton to find a convenient telephone and call his boss. "I'm somewhere back of old Lysee's herb shop. It's a matter of life and death. There's a secret panel on the back of the counter. You better come well heeled. These babies don't play with marbles." Nigh was no stranger to directing movies about Asians with white actors impersonated Orientals. He directed all five Boris Karloff mysteries in the "Mr. Wong" franchise: "Mr. Wong, Detective," "The Mystery of Mr. Wong," "Mr. Wong in Chinatown," "The Fatal Hour," and "Doomed to Die." Later, Nigh directed Lugosi again in "Black Dragons" during 1942.
Of course, "Dracula" star Bela Lugosi was atrociously miscast as Mr. Wong with his obvious Hungarian accent. More than likely, Monogram cast Lugosi because Universal had cast Bela's biggest rival Boris Karloff in their 1932 epic "The Mask of Fu Manchu." Nevertheless, Bela delivers his lines with reasonable credibility and doesn't bump into the furniture. He looks pretty sinister as an Asian villain and he is up to his ears in intrigue and murder. "The Mysterious Mr. Wong" wallows in racial prejudice that was part and parcel of its time. Nevertheless, it still ranks as an entertaining B-movie.