24 January 1970: broadcast of fourth episode of Spearhead from Space. The Doctor and Liz defeat and expel the Nestene Consciousness, and the Doctor accepts the Brigadier's proposal that he become UNIT's Scientific Adviser.
24 January 1976: broadcast of fourth episode of The Brain of Morbius. Morbius arises; the Doctor defeats him in a mind-bending contest; and the Sisterhood force him over a cliff, but restore the Doctor's life.
24 January 1981: broadcast of fourth episode of Warrior's Gate, last appearance of Romana II and of K9 Mark II on TV. Rorvik blows up his own ship, inadvertently freeing the Tharils and allowing the Doctor and Adric back into N-Space; but Romana and K9 stay behind.
(Compare and contrast these three stories, each of four episodes, broadcast on exactly the same dates in three different years.)