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The TARIS(sic) narrowly avoids becoming engulfed in a web-like substance in space. It then arrives in the London Underground railway system, the tunnels of which are being overrun by the web and by the Great Intelligence's robot Yeti. The time travelers learn that this crisis was precipitated when Professor Travers, whom they first met in the Himalayas some forty years earlier, accidentally caused one of the Yeti to be reactivated, opening the way for the Intelligence to make another invasion attempt.