At the time the First Doctor visited with Susan, Barbara Wright and Ian Chesterton, the Conscience of Marinus machine was hidden on Marinus, and there were acid seas and glass beaches on the planet. By then, it has also been invaded by the Voord, under the leadership of Yartek. (TV: The Keys of Marinus, AUDIO: Domain of the Voord) The Daleks came to Marinus and fought the Voords until they learned of the Voords' knowledge of the Great Power and joined forces with them. They captured the First Doctor, who had also travelled to Marinus. (PROSE: Doctor Who and the Daleks)