The Sentinels was a story by Malcolm Shaw and Mario Capaldi which ran in Misty from 4th February to 22nd April 1978. It concerns the Richards family, and more particularly young Jan Richards, who start squatting in a derelict tower block with a sinister reputation after being made homeless, and discover that it is a gateway to a terrifying alternate reality where Britain as been occupied by Nazi Germany since 1940. The story is frequently disturbing, particularly given that it was aimed at an audience of pre-teens, with a sequence in which the heroine's pet dog, Tiger, sacrifices himself to save her and is eaten alive by giant rats being especially horrific. The story ends with our heroes making it safely back to their own word and destroying the gateway, though the Nazi Earth remains intact and Jan's father's heroic counterpart on that world is left in the hands of Nazi torturers.
The story was revisited in Return of the Sentinels by Hannah Berry and Ben Willsher in the 2017 Scream! & Misty Halloween Special, in which a girl called Jennifer discovers that the tower is now a gateway to a fascist Britain where racial segregation exists and Muslims have apparently been exterminated.
The story was reprinted in Misty (Collected Edition) Vol 1 2.