The Sentinels and End of The Line. The two identical tower blocks, known as `The Sentinels' to the locals, stand tall over the town of Birdwood - but only one is occupied while the other remains mysteriously empty. When Jan Richards' family lose their home they decide to hide out in the abandoned block so they can stay together, only to be sent into a parallel world where the Nazis conquered Britain in 1940... In End of the Line, Ann's father was one of a group of engineers believed to have been killed whilst working on an extension to the London Underground but when she and her mother are invited to the opening of the new train tunnel, Ann discovers a mysterious time portal through which several workers are being kept as slaves by an evil Victorian called Lord Vicary.