The Doctor goes to Logopolis to repair the TARDIS' chameleon circuit, not knowing that a shadowy watcher is spying on him. Meanwhile, his old enemy the Master has only recently gained secure longevity by possessing the body of Tremas, and revels in his safety. He has plans of his own for the planet of mathematicians, Logopolis, and a plan that could spell doom for the entire universe. The Master's plan could rock Logopolis, the keystone of all life. Could this mean the unravelling of the causal nexus and the end of the universe itself? The Doctor must pit his wits against the Master in a desperate battle to thwart his plans. But he is aware that this might be a fight which could easily spell the end of his life.