The future? The Earth is dying under the onslaught of industry, the polar caps are melting, the ozone layer is nearly destroyed... To save the planet, the Doctor must overcome the combined forces of some of the most feared of his old adversaries. But he must also confront a far greater enemy - one that has already reverted him to his Fourth Incarnation - in order to save both the past and future Doctors before they are taken out of time and cease to exist.