premise: The twenty-first season of British science fiction television series "Doctor Who" began on 5 January 1984 with the 5th Doctor (Peter Davison) serial "Warriors of the Deep", and ended with Colin Baker's first serial "The Twin Dilemma". For only the second time (the first being during season 4), the entire TARDIS crew changed over the course of a single season.
hypothesis: The Warriors of the Deep and The Twin Dilemma were both the first and last shows of the series. 
reason: The statement both makes sense and doesn't make sense.