The Best Episodes Written By Gerry Davis

In 1986 a new planet appears in the Solar System which turns out to be a long-lost twin of Earth's named Mondas. Its inhabitants are the Cybermen.

What if a man-made virus with the power to melt all plastic became as infectious as the common cold? When a plane crashes in South America, in quite extraordinary circumstances, it's up to Dr Quist's team to avert further disaster.

The Doctor, Harry and Lester try to destroy the Cybermen's relay device, while the Vogans prepare to destroy Nerva even though Sarah Jane is still on board.

Doomwatch are joined by Doctor Robson, sent to undertake tests on the new 'Sahara' spray which is apparently capable of destroying all plant-life on the planet. But when Quist receives a phone call from the ministry, he is given orders to immediately suspend both Robson and Toby without any explanation. Closer investigation leads Quist and his team to discover that a new computerised security system run by Commander Keeping and Barker has become far too powerful, and is making its own decisions about government personnel.

The orbit of Jupiter, the 25th century. Arriving back on the Nerva Beacon much earlier in history, the Doctor and his friends discover the satellite beset by space plague while its crew struggles to keep space traffic away from Voga, the newest moon of Jupiter. But what is the connection between Voga, the plague, and some old enemies of the Doctor?

The Doctor transmits Sarah Jane and Harry down to Voga to cure Sarah Jane of the Cybermat's poison but Kellman's sabotage means he is unable to bring them back.

The Cybermen force the Doctor, Stevenson and Lester to carry bombs to the centre of Voga while Sarah Jane, Harry and Tyrum decide to contact Vorus.