Continuity mistake: When the butler shows up at Steed's apartment to kidnap Tara, they fight and her culottes are unfolded at the knee. After he has knocked her out and put the last jigsaw pieces in the puzzle, he goes to pick her up to carry her out, and her culottes have been folded up at the knees with no way for that to have happened.
Continuity mistake: When Steed is waiting to catch Mother's special bus. Steed has parked his car fully in the road and by a bus stop sign. As the bus arrives and parks at the kerb, Steed's car has vanished - the bus would otherwise have collided with it.
Continuity mistake: After being hit by the amnesia dart, Steed falls unconscious with his bowler hat still on his head. But when the enemy agent approaches and shoots him again, his hat is off and he's lying in a completely different position. (00:21:00)