Doctor Who and the Revenge of the Cyberman — Terrance Dicks

THE CYBERMEN

One by one, their limbs became diseased--they were replaced by plastic and steel! Little by little, their brains tired--computers worked just as well!

Locked in a battle once again with these dreadful Cybermen, Doctor Who is caught between desperate Vagans, determined to save their planet, Voga, and the Cybermen, determined to destroy it. But Doctor Who has one last trick up his sleeve: it is a poison--powerful, plentiful, and deadly. And it is the only weapon humans have against the Cybermen, and the only reason the Cybermen must destroy Voga--the planet of Gold.