Circle line

The Circle line was a line on the London Underground. It was the major focus of the Great Intelligence's attack on the Underground. British Army Corporal Blake and Craftsman Stephen Weams monitored a map of the Underground with the Circle Line emphasised to show the Yeti's progress. That growing black line showed that King's Cross, Embankment, Paddington station and Euston Square were under apparent Yeti control.

When Jamie McCrimmon read a map of the line on the Cannon Street platform, he discovered that three consecutive stations on the line were Cannon Street, Monument and Tower Hill. (TV: The Web of Fear)