Continuity mistake: When Virgil radios to Jeff that he is about to land on Mount Arkon, Jeff asks him what the weather's like, to which Virgil replies: "Pretty stormy, Father. Pretty stormy." Then we cut to an exterior of the airborne Thunderbird 2, which is absolutely covered in snow. Just moments later we get a long shot and suddenly Thunderbird 2 is no longer covered in snow. We then get a close-up of the cockpit view, where we see Virgil and Brains, and Thunderbird 2 is covered in snow again. We soon get another couple of shots where it alternates between Thunderbird 2 not snow-covered and then being covered in snow again. (00:28:00)
Continuity mistake: As Alan makes his telecall to Grandma, the close-up of his hand dialing her number shows the push-button dial panel with letters on the left and numbers on the right, but on the puppet-sized telecall unit, the numbers are on the left and the letters are on the right.
Continuity mistake: During the after-mission chat, Alan is wearing a bandage above his left eye due to an injury he picked up on duty. If you look carefully this bandage sometimes changes between shots; it is particularly noticeable when he's in the bathroom with Tin-Tin. Also, the bandage is too small and too high up to have covered the injury adequately. (00:45:25)
Continuity mistake: When Alan, Tin-Tin and Scott are lowered while on the settee to enter Thunderbird 3, looking head-on at them we have the three of them sat in that order from left to right as they descend the shaft. However, when it cuts to the long shot, Alan and Scott have magically swapped places. When they are fully raised into Thunderbird 3, Alan and Scott are back in their original positions on the settee. (00:18:50)
Factual error: On the night of the Hudson Building fire, the Auto Date Fixer in Commissioner Garfield's office reads 12/7/65. The next day, it reads 13/7/65, illustrating attention to detail on the part of the set decorator. Unfortunately, this overlooks the American convention for the month numeral to appear first. In the US the convention is month/day/year, in the UK the convention is day/month/year. So,either the first date should read 7/12/65 (July 12th) with the next day as 7/13/65, or the second date should read 12/8/65 (December 8th).
Plot hole: When Jeff Tracy contacts Lady Penelope, it is 10:00am in England, yet it is already daylight on Tracy Island in the South Pacific and Alan, Gordon and Tin-Tin have been out fishing for some time. (It is later established in the 1966 "spin off" movie "Thunderbirds Are Go" that there is a five hour time difference between Tracy Island and England. So, using that as a guide, when it's 10am in England, it should be 5am on Tracey Island.)
Deliberate mistake: Throughout Thunderbirds, when the script required objects to be manipulated, there were cutways to close up 'insert' shots of real human hands - usually of the puppeteers/crew. However in this episode, Alan's close-up (i.e. live action) hand is remarkably hairy with very dark hair. Yet Alan Tracey is supposed to be 21 and blond haired (including the hair on the back of his hands).