A Visit from Blackmer
Dr. Orchard and his assistant, Hector McGill, live in a lonely house on the Ambro River. Orchard has found a rare plant (Sidonicus americanus), that grows only in this part of the Ambro River. From it, in his laboratory, Orchard has developed a food additive called theramine, which greatly increases the size of animals fed with it. This discovery obviously has great potential as a solution to the world food shortage, and even greater financial implications.
He invites Blackmer to his home to show him his discovery.
A Violent Storm
Sitting in the lounge, the trio listens as the storm rages.... Doors creek and light dim, the door swings open and a ghostly sight is seen at the top of the stairs. McGill goes to investigate, and to his relief finds it's only Mrs. Files lit up by lighting, coming through the window.
A Worrying Discovery
In the morning Dr. Orchard is called to his Laboratory by his assistant Hector McGill who has noticed that the Theramine has been tampered with. Seconds latter they hear gun fire and screaming coming from the river, they race to the front door to investigate.
McGill Is Sent on a Rescue
A Close Escape from the Laboratory
Dr. Orchard, Hector McGill and Mrs. Files shelter in the basement laboratory, which very quickly becomes unsafe as the alligators attack the house. Dr. Orchard is struck by a falling beam that knock him to the ground. As the building continues to crumble they move upstairs, hoping it would be safer.
Scott manages to gain entrance to the house through a side window but is taken by surprise by Culp who Using a secret underground passageway built by the previous owner.
Merging from behind a bookcase he shoots Scott's gun from his hand and disarms him. Culp intends to make a getaway with Dr. Orchard's Theramine, threating to pour it into the swamp unless he is given clear passage. He sets off in Dr. Orchard's Motor Launch. Suddenly a fourth alligator attacks Culp's boat and he is thrown into the swamp, Scott and Orchard watch in horror as the phial is lost into the swamp.