Plot hole: In order to build up suspense, Virgil and Brains stand on the Crab Logger as its dangerous fuel is pumped out, despite the fact that it is hanging on the edge of a precipice. In fact they could have left as soon as they had plumbed in the pipes to empty the fuel tanks - the whole procedure is controlled by Scott in Thunderbird 1 and they make absolutely no contribution to the operation at all. They do not need to disconnect the pipes; they are left behind and dropped from Thunderbird 1 as planned. They just stand there chatting about how much danger they are in until jumping clear at the very last second. Silly buggers.
Continuity mistake: When The Hood drives his van off the broken bridge whilst escaping the police, watch carefully; the van bounces off the rocks on the other side and starts to fall roof-first into the river below. However, when it cuts to the van falling into the water it falls in upright.
Continuity mistake: When Thunderbird 2 leaves the hangar on Tracy Island, it appears that Pod 3 has been selected (Pod 2 is visible to the right of Thunderbird 2), yet when Virgil and Brains arrive at Mount Arkan, the Transmitter Truck emerges from Pod 6. (The same continuity error also occurs in the episodes 'Vault Of Death', 'Move - And You're Dead', 'Martian Invasion', 'The Perils Of Penelope' and 'Day Of Disaster', probably due to the same footage being re-used for those episodes).
Continuity mistake: When Alan contacts his father at Tracy Island, Jeff asks him "How's the situation, boy?" Alan informs him that Grandma has passed out in the heat and Alan's face is covered in sweat. But after a quick cut to Jeff saying "Passed out?" we return to Alan, and the sweat on his face has disappeared.
Other mistake: As Virgil prepares to clear the wreckage of the tower from the rescue area using the Firefly, Scott tells him that he will go over to Thunderbird 2 to prepare the Mole for tunneling. The Tower Controller then says to Scott, "I've got a fast car ready for you outside" without moving his lips.