Revealing mistake: When the Doctor goes into the CET projection of Eden, to fight the Mandrells, he disappears into the bushes on the left-hand side of the screen. Cue much shaking of foliage, and Tom Baker's cries of 'ooh', 'aargh' and 'ouch'. The Doctor then reappears with his clothes all tattered and torn, due to his 'fight' with the Mandrells...but the the fact that there is not a mark (not even a scratch) on Tom Baker is something of a giveaway that all Tom Baker did was disappear behind some bushes and do a quick change into a tattered version of his costume.
Visible crew/equipment: In episode 2, as K-9 seals the wall panel, watch out for the hand which emerges to hold it in place.
Revealing mistake: Watch the Mandrells closely, especially in the later parts of the story: one of them seems, at one point, to have forgotten to zip up the back of his costume.
Revealing mistake: In the very first shots of this Doctor Who story, it is obvious that the "Empress" Spaceliner is a model - you can even see the stick that holds the model in place.
Plot hole: When Della gets shot in the face in episode four, she clutches her stomach. (What is even more remarkable about this error is that this keeps happening over and over again: someone gets shot and falls to the ground, clutching their stomachs, regardless of where they have actually been shot. See the error in Season 14's 'The Deadly Assassin' for an example of the SAME error occurring).
Revealing mistake: Geoffrey Hinsliff (playing Fisk) accidentally refers to Tryst as "Fisk" at one point.
Continuity mistake: When the Doctor finds the vraxoin vial in episode 1, he puts it in his right coat pocket, from where it is then removed by Stott. However, at the end of episode 2, Costa's scanner finds vraxoin traces in the Doctor's LEFT coat pocket.
Revealing mistake: During the whole story, Tom Baker is struggling not to laugh at Tryst's completely made-up accent.
Answer: Your right it is, "Island of Terror."