text:  The Second Doctor previously encountered the Great Intelligence in the serials The Abominable Snowmen ( 1967 ) , set in the 1930s , and The Web of Fear ( 1968 ) , set in the 1960s . In these stories , the Great Intelligence uses robot Yeti as its physical presence . The events of The Web of Fear are alluded to by the Doctor in " The Snowmen " when he presents the London Underground biscuit tin to the Great Intelligence in Dr Simeon 's laboratory ; the Intelligence states , " I do not understand these markings " , in reference to the 1967 London Underground map design on the tin . The Doctor remarks that the Underground is a " key strategic weakness in metropolitan living " , referring to ( and possibly setting in motion ) the future Yeti attack on London via the Underground . 
  