Attack Of The Alligators! is the 24th produced, and the 23rd broadcast, episode of the British television series Thunderbirds.
Blackmer visits Dr Orchard and his assistant Hector McGill at a lonely house on the Ambro River to see the effects of a new food additive called theramine, developed by Orchard from a rare plant that only grows in this area. Theramine greatly increases the size of animals fed with it, offering a solution to the world food storage and even greater financial potential. These revelations are overheard by the boatman Culp, who later steals a sample of theramine from the laboratory, accidentally spilling some of the drug into the sink. He washes the spillage away into the river where it immediately affects the growth of three alligators. When Culp ferries Blackmer down the river the next morning, they are attacked by one of the alligators, now grown to enormous size. Blackmer is rescued by McGill but when they take refuge in the house with Orchard and his housekeeper Mrs. Files, they are surrounded by all three of the giant creatures.
Attack of the Alligators! on Thunderbirds Wiki: