Complex sentence: It features the Sixth Doctor and Mel, with the villain being the Master-as well as featuring a brief appearance by an alternate version of the Third Doctor -, and is a sequel to the 1972 television serial "The Time Monster".
Split into simpler sentences: It features the Sixth Doctor and Mel, the Master, and an appearance by an alternate version of the Third Doctor. It is a sequel to the 1972 television serial "The Time Monster".