 only four  of the series 26 seasons (the 8th, 22nd, 25th and 26th) did not  include an arriving or departing regular cast member. Only two  regular characters did not get a departure scene: the character of  Dodo Chaplet disappeared halfway through the 1966 serial "The War  Machines"; the character Liz Shaw simply did not return after the  1970 season. The departures were explained in dialogue in subsequent  episodes. Actors Mary Tamm (qv) and Colin Baker (I) (qv) did not  get leaving scenes 