A Sixth Doctor novel with Peri Brown. With Peri in danger of losing her arm - maybe her life - the Doctor has no choice but to return to a planet form his past, Karn, at the strategic heart of a galaxy of perpetually warring planetary alliances. Centuries of battle have trained the surgeons of Karn to incredible heights of medical skill, and besides, it is also the home of the mysterious Sisterhood, rumoured to possess the elixir of life. The top surgeon of the planet is an ambitious young man by the name of Mehendri Solon... Why is Solon so determined to keep his Project Z a secret at all costs? Who is the General, whom the Doctor suspects of being a fellow Time Lord? When the answers to these questions are clearly revealed, the Doctor is commissioned by Gallifrey to fulfil a role entirely alien to him - he becomes the Supremo, ruthless and dedicated in his struggle to forge an alliance of disparate planets against the threat of profound evil. But given that he is living in his own past, how far can he afford to affect the future?