Blood Beast

Plot
In 19th century Britain, a series of grisly murders are taking place in the countryside near London. The victims are good-looking young men, between the ages of twenty and thirty and all have had their throats torn open and blood drained. The witness of the latest murder, coachman Joe Trigger, is driven insane when he catches a glimpse of the mysterious killer.

Investigating the deaths are Detective Inspector Quennell of Scotland Yard and his assistant, Sergeant Allan. Because Joe keeps ranting about a horrible winged creature with huge eyes, Quennell hatches a theory that perhaps an eagle is on the loose. At the scene of the latest killing, several large scales are discovered.

The two latest victims were students of the renowned entomology professor Dr Carl Mallinger, who lives nearby with his beautiful daughter Clare and their scar-faced butler, Granger. When Quennell brings the scales to Mallinger for identification, Mallinger behaves suspiciously and tries to take all of them. Quennell describes his theory about a killer eagle, but Mallinger dismisses it outright. Quennell is unaware that the entomologist has a pet eagle, which the sadistic Granger torments.

Explorer and naturalist Frederick Britewell returns from Africa with some moth chrysalids for Dr Mallinger and the handsome young adventurer soon falls victim to Clare, who is the real murderer; Clare is a "were-moth" and transforms at night to drink the blood of young men. Britewell becomes her latest victim after watching her in an amateur horror play performed by some of her father's students (which seems to be a spoof of the Hammer Frankenstein genre[citation needed]) but lives long enough to exclaim 'deaths head' to Quennell before he dies. Both Mallinger and Clare claim not to have known Britewell when questioned by Quennell.

Quennell's superior suggests he takes a holiday and delegate the case to Sgt Allan, but the Detective Inspector refuses. He reveals his intention to send his daughter Meg to stay with some relatives in Sussex until the investigation is over. As they leave for the railway station, Allan informs Quennell that Dr Mallinger did in fact know Frederick Britewell, prompting Quennell to perform an immediate search of Mallinger's home. He finds that the scientist and his daughter have left for Upper Higham. He also discovers a cellar filled with human bones and Granger's corpse.

Quennell informs his superior he will be taking leave after all: he and Meg go to Upper Higham incognito as a vacationing banker named Thompson and his daughter. There they meet a young insect collector who shows him the proudest exhibit in his collection, a Deathshead moth and Quennell discovers that Mallinger is also incognito as a Dr Miles staying at a nearby estate. Mallinger is attempting to create a male were-moth to be a mate for his increasingly bloodthirsty daughter.

Clare kidnaps a child to provide blood for the male were-moth, which is growing in a cocoon. After this, Mallinger decides to end the experiment, burning the cocoon, which prompts Clare to assume moth form and kill him.

Quennell arrives at Mallinger's house with a police officer and finds Clare in moth form attacking another victim. After Clare flies up to escape the scene, Quennell lights a fire in the garden, prompting her to fly back down into it, where she is consumed by the flames.