The place is the country house of Courtleigh Fleming, the late President of the Union Bank. When his nephew Dick rented it to Cornelia Van Gorder, a spinster of 60, she expected her stay there to be a restful four months, enlivened by the occasional guest and some homemade elderberry wine. Instead, intruders and anonymous threatening letters left her hardly able to sleep at night, and newspaper stories about a mysterious nocturnal criminal known as "The Bat" only added to her worries. These disturbances were already too much for the weak nerves of Lizzie Allen, maid to Miss Van Gorder for twenty years, who would have packed up and left if Cornelia had allowed her. The cook, parlormaid, and housemaid had nothing stopping them from being frightened away from the house; each offered an unbelievable excuse for leaving. Besides Lizzie, the only servants left in the house were Billy, Courtleigh Fleming's Japanese butler, and Brooks, allegedly a new gardener but obviously no gardener at all.
Cornelia phones Police Headquarters, and a detective, Mr. Anderson, is sent over to the house. Arriving before the detective are Dale Ogden, Cornelia's pretty young niece paying an unanticipated visit, and Dr. Wells, the doctor who recently witnessed Courtleigh Fleming's death in Colorado and seems all too eager for Cornelia to leave the house with him. Cornelia, worried but determined to stay, orders the butler to let no more visitors in after Mr. Anderson, but more break-ins will happen later.
One unanticipated visitor is already in the house: Jack Bailey, alias Brooks, the cashier accused of the million-dollar theft which caused the Union Bank's recent failure. Secretly engaged to Dale, he tells her that it was Courtleigh Fleming, not him, who took the money out of the bank and stashed it in a Hidden Room built into the house. Dale gets the idea that Fleming's nephew would know where the blueprints are, and places a telephone call. Richard Fleming is driven over to the house in a hurry by a lawyer named Reginald Beresford. Dick finds the wanted blueprint, struggles over it with Dale, and is shot and killed. The shot came from the same staircase which Lizzie had earlier seen a ghost going up.
As the detective starts asking questions, a strange voice is heard groaning dreadfully over the house phone. The Calling Card of The Bat appears in the house, reminding Lizzie of Anderson's words in the paper: "He may be a merchant—a lawyer—a doctor, honored in his community by day—and at night a bloodthirsty assassin." The doctor makes a suspicious grab for the scrap of blueprint found in Richard Fleming's hand. Cornelia decides to do some detective work of her own, concerning the staircase. And an unknown man staggers in, not knowing who beat him and tied him up or even his own name.
The play was first produced in 1920, and became an international hit. It spawned a Novelization, and was adapted to film in 1926, 1930 and 1959. The 1930 film adaptation, titled The Bat Whispers, was cited by Bob Kane as one of the inspirations that led him to create Batman.
Not to be confused with Die Fledermaus.
- Affably Evil: Dr. Wells in the 1959 version. He murders John Fleming when Fleming admits he embezzled one million from his bank, followed by suggestion that Wells should help him fake his death so he could get the money in exchange for half, or he'd kill Wells to keep him quiet. Beyond that, any evilness on his end appears as him warning Cornelia to get out of the Oaks because of its bad history so he can get the money, and it turns out he's not the Bat.
- Almost Out of Oxygen: In the 1959 version, Cornelia almost suffocates when the door of the secret room closes, trapping her inside, and she cannot find the switch to open it.
- Antagonist Title: The Bat is a Serial Killer who is terrorising the inhabitants of an Old, Dark House.
- Big Damn Heroes: Warner, in the 1959 version, arrives and shoots The Bat, revealed to be Lieutenant Anderson before Anderson can murder Cornelia, Lizzie and Dale.
- Bitch in Sheep's Clothing:
- Dr. Wells murders John Fleming to steal the million Fleming embezzled, though Fleming planned on murdering Wells if he didn't cooperate.
- John Fleming embezzled a million dollars from his bank and framed the cashier and planned on murdering Wells if he didn't cooperate (and may have been planning to murder him anyway to silence a possible witness).
- Lieutenant Anderson is The Bat.
- The Blank: The Bat wears a featureless mask (although up close it can be seen that it has eyeholes). This causes witnesses to describe him as being without a face.
- Calling Card: The bat symbol comes in many forms.
- Changed My Mind, Kid: Warner in the 1959 version arrives just as The Bat is about to Leave No Witnesses. Warner then explains he was on his way to the airport and changed his mind.
- Coat, Hat, Mask: The Bat's outfit consists of a black fedora, black suit and black featureless mask.
- Cool Old Lady: Cornelia, especially in the 1959 version where she's written as a famous mystery novelist who takes it upon herself to figure out what the Bat's up to.
- Cut Phone Lines: The Bat disables both the internal and external phones when he breaks in to search for the secret room in the 1959 version.
- Faux Affably Evil: John Fleming from the 1959 version. He starts off a rather amicable conversation with Wells about how he stole the money and framed the bank manager, but then leads into a cold blooded discussion about murdering an innocent man and disfiguring the body so John can fake his death and retrieve the stolen money. If it hadn't been for that forest fire catching him off guard, John may have very well killed Wells if he didn't cooperate (and possibly even if he did).
- Genre Savvy: Cornelia applies her expertise in mystery novels to what's going on around her concerning the Bat and the missing money.
- Gun Struggle: In the 1959 version, one occurs between the Bat and Dr. Wells. Dr, Wells winds up dead.
- Handy Cuffs: This mistake is performed twice on the same person. The second case, in which the character manages to seize a gun with his cuffed hands, is egregious because the cuffs were put on by the real detective.
- Heterosexual Life-Partners: Cornelia and Lizzie have shades of this in the 1959 version with a few moments of Les Yay, surprising considering their respective ages and the decade the film was made in.
- Hollywood Glass Cutter: In the 1959 version, the Bat uses a small blade to cut a hole from a glass-paned door, which he then unlocks and opens by reaching inside.
- Hysterical Woman: Lizzie. While this is still there in the 1959 version it's also somewhat downplayed. One reviewer has claimed the 1959 Lizzie was much more bearable than the previous two.
- Mama Bear: In the 1959 version Cornelia begins to take on this role for Dale after Judy is killed.
- Mystery Writer Detective: In the 1959 film version, Cornelia is rewritten as a mystery writer renting the mansion for some inspiration, which she gets in spades.
- Old, Dark House: The Oaks in the 1959 version is a huge mansion in the countryside. It's by no means decrepit or creepy looking during the day, but at night its enormity can be rather unsettling.
- Pants-Positive Safety: In the 1959 version, John Fleming shoves the pistol he intends to use on Dr, Wells down the front of his pants.
- Peekaboo Corpse: In the 1959 version, Dale finds Mark Fleming's body stuffed into the secret closet behind the grandfather clock; his throat slashed.
- Police Are Useless: In the 1959 film adaption. Of course the police lieutenant is useless, because he's the Bat.
- Slashed Throat: This is how the Bat murders his victims; slashing their throats with his steel-taloned glove.
- Slipping a Mickey: In the 1959 version, Davenport—the detective left on duty to watch the house—has his wine drugged, causing him to pass out.
- Stating the Simple Solution: When the detective is puzzling over which panel to strike to open the sealed room Cornelia's trapped in, Lizzie asks what difference it makes and strikes all of them until she hits the panel that opens the room.
- With Catlike Tread: In the 1959 version, the Bat sneaks into the house, disables the telephones, and creeps past the sleeping occupants, only to then start chiselling his way through a wall.
- Wolverine Claws: The Bat's signature weapon are claws mounted on the fingers of his gloves which he uses to slash his victims' throats.