A scientist named Orchard is performing experiments with a rare plant in order to improve the meat production of
animals. An associate, Mr. Blackmer, is coming to review the progress, but the house that Orchard lives in is only
International Rescue are out of radio contact with the world, and Thunderbird 2 is launched to fly Alan up to the radio mast to
repair it. The fault is due to a worn component, and contact is soon restored, much to John's relief in Thunderbird 5.
A storm whips up, and Blackmer cannot leave Orchard's house. He and the boatman, Kalp are put up for the night. The housekeeper,
Mrs. Fyldes, cannot take to Kalp, who soon steals the keys to the laboratory from her room. He steals a test tube of the
chemical, theramine, but accidentally spills the rest down the sink, and tops up the beaker from a conical flask nearby.
Next morning, Blackmer leaves. Orchard's assistant, McGill finds that the theramine has been exchanged, as giant alligators
attack the boat, which is destroyed. Blackmer survives and is rescued by McGill, but the alligators turn their attention on the
house. Everyone moves downstairs into the basement lab and call International Rescue.
When Scott arrives on the scene, he manages to scare the alligators away, giving him time to land and get into the lab. Mrs.
Fyldes reveals that there is a secret exit to the house, and that only Kalp and the previous owner, Lopez, knew where it was. In
the lounge area, Kalp emerges from the secret passage behind a bookcase and holds them all hostage.
Thunderbird 2 arrives, and Virgil scares the returning alligators away with the VTOL jets. Gordon and Alan shoot two of the
alligators with tranquilizers, but the third escapes. Alan sets off after it on his hoverbike to head it off, away from the house.
It works, but he doesn't look where he's going, hits a tree and falls off. Fortunately, Gordon manages to shoot the alligator
before Alan is eaten.
The trapped people escape, but Kalp is attacked by another alligator, and the theramine phial falls into the river. Gordon is able
to retrieve it intact before any more damage is caused.
Back at Tracy Island, TinTin gives Alan an early birthday present - a pygmy alligator!
Trivia: Virgil picks up Pod 6, but Thunderbird 4 is on hand when
they need it.
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