Complex sentence: In "The Real Thomas", Thomas is revealed to be a Russian spy whose real name is Nicolai and leaves the park and goes on the run, for as he said "Once a spy, always a spy".
Split into simpler sentences: In "The Real Thomas", Thomas is revealed to be a Russian spy whose real name is Nicolai. In this episode he leaves the park and goes on the run, with the justification, "Once a spy, always a spy".