Ev, along with her husband, Harold, and their lawyer friend Martin, are scuba diving while on vacation in Puerto Rico. When they resurface, they gradually conclude that an unexplained, temporary interruption of oxygen has killed everyone on the island... maybe even the world.
Demonstrating that a little knowledge is a dangerous thing, a convicted strangler studies the paranormal and finds a way to render himself invisible. Once he escapes, he sets out to find and eliminate the five women who testified in his prosecution. A police lieutenant (Robert Foxworth) sets out to safeguard them, and bring the invisible killer to justice.
Rival newspaper reporters Pat Morgan and Ted Kord find themselves unraveling the mystery behind the death of a millionaire philanthropist who fell from his penthouse balcony. When it is discovered that the plunge was not an accident, the building's residents come under suspicion. Soon, the body count begins to mount as three more murders occur by strangulation.
When her husband John has a heart attack while out in a rowboat on the lake, Louise Haloran throws his body overboard and later tells the family that he has left on an urgent business trip. Her main concern is that she can only inherit a part of the family fortune if her husband is alive. The Halorans are a strange family, still grieving over the death of the youngest daughter Kathleen who drowned in a pond when she was just a child. They hold an annual ceremony of remembrance every year on the anniversary of her death. This year however, someone is wielding an ax intent on murder.
When an escaped circus gorilla appears to have gone on a murderous rampage, a threatened attorney calls on the detective trio of Garrity, Harrigan and Mullivan to act as bodyguards. In short order, we discover that there is more to the attorney than meets the eye, and the ape may be innocent after all. When a pretty young heiress faces peril, it's up to our heroic trio to save the day.
When the villagers of Klineschloss start dying of blood loss, the town fathers suspect a resurgence of vampirism. While police inspector Karl remains skeptical, scientist Dr. von Niemann cares for the vampire's victims one by one, and suspicion falls on simple-minded Herman Gleib because of his fondness for bats. A blood-thirsty mob hounds Gleib to his death, but the vampire attacks don't stop.
Mystery writer Cornelia Van Gorder has rented a country house called "The Oaks", which not long ago had been the scene of some murders committed by a strange and violent criminal known as "The Bat".Meanwhile, the house's owner, bank president John Fleming, has recently embezzled one million dollars in securities, and has hidden the proceeds in the house, but he is killed before he can retrieve it.
Dr. Bill Cortner and his fiancée, Jan Compton, are driving to his lab when they get into a horrible car accident. Compton is decapitated. But Cortner is not fazed by this seemingly insurmountable hurdle. His expertise is in transplants, and he is excited to perform the first head transplant. Keeping Compton's head alive in his lab, Cortner plans the groundbreaking yet unorthodox surgery. First, however, he needs a body.
Mary Henry ends up the sole survivor of a fatal car accident through mysterious circumstances. Trying to put the incident behind her, she moves to Utah and takes a job as a church organist. But her fresh start is interrupted by visions of a fiendish man. As the visions begin to occur more frequently, Mary finds herself drawn to the deserted carnival on the outskirts of town. The strangely alluring carnival may hold the secret to her tragic past.