Recap: Thunderbirds S 1 E 8 Desperate Intruder
Tin Tin and Brains meet up with an archeologist friend to investigate the ancient temple at the bottom of Lake Anasta. While seemingly safe, they are in fact under observation by their old foe, the Hood. Using the unspeakable power of his glowing yellow eyes, the Hood attempts to torture the location of the temple's treasure out of Brains, but he's unable to do so before International Rescue turn up to save the day.
However, determined to prove his theories correct and make amends for causing trouble, Brains sneaks out in the night and swims back to the temple, where he is again accosted by the Hood and left to die. Thunderbird 4 manages to rescue Brains before his air supply runs out, and while the Hood escapes, he's forced to do so without his treasure.