When a Nestene Energy Unit is stolen and a radio telescope sabotaged, the Doctor is contacted by a Time Lord who tells him his old rival the Master is responsible.
Did You Know?
3 years earlier in the 1968 Patrick Troughton story "The Mind Robber", The 2nd Doctor learns that the man in charge of The Land of Fiction is called The Master. This was a foreshadowing of The Master in Series 8. However, The 2nd Doctor may had thought that The Master whom was in charge of The Land Fiction was the evil Time Lord himself. The 2nd Doctor's reaction when he is told about The Master hinted at this. See more
[the lab apparatus the Doctor is working on catches fire, so Jo puts it out with a fire extinguisher
You've ruined it!
But your bench was on fire.
Three months delicate work and now look at it, you ham-fisted bun vendor!