Q is for... Quinn

Dr John Quinn was chief scientist at the Wenley Moor research centre, built beneath the Derbyshire countryside. Here, a Cyclotron was being developed which could produce vast amounts of cheap electricity. UNIT were brought in to provide additional security after a series of nervous breakdowns were reported amongst the staff, accompanied by unaccountable power losses. Two of the staff who went potholing in the nearby cave systems were then involved in an incident which left one dead and the other mentally disturbed. Quinn knew the cause of these incidents, but confided only in his friend and fellow scientist Miss Dawson.

He was also a keen potholer, and during one of his expeditions he had discovered a race of intelligent bipedal reptiles, living in a shelter built within the cave system. They were the ancient race of Silurians, who had ruled the Earth before the ascent of the human race. Eager to learn from them, he agreed to assist them in syphoning off power from the Cyclotron to reanimate their hibernating kin - promised scientific secrets in return. He carried out small acts of sabotage, such as tampering with the centre's logbooks so no pattern in the power losses could be discerned.

When one of the Silurians was wounded and forced onto the moors, they sought his help in rescuing it. He was given a summoning device which would attract it to him. After the creature had attacked and killed a farmer at a remote farm, the Doctor and Liz Shaw became suspicious of him as he appeared to have driven well out of his way to visit the scene. UNIT troops then heard the summoning device being activated, and tyre marks indicated that Quinn had been in the vicinity.

The Doctor went to his cottage and found the temperature inside extremely hot, which Quinn dismissed as due to a faulty thermostat - but the scientist had already told Miss Dawson that he had found the Silurian and was going to hold it hostage until its people gave him the knowledge they had promised.

Guessing as much, the Doctor tried to talk him into co-operating with him, but Quinn declined.

The wounded Silurian recovered and killed him.

Played by Fulton Mackay. Appearances: The Silurians (1970)

• Mackay was a strong contender to replace Jon Pertwee as the Fourth Doctor. Producer Barry Letts had met him at a dinner party hosted by Roger Delgado and was impressed by him. However, he was worried that he would give an acting performance as the Doctor, whereas what he really wanted was a natural eccentric whose personality would feed into the role. It became a moot point anyway as Mackay had recorded the pilot for a prison-set sitcom - Porridge - starring Ronnie Barker, and this was to go into series. Mackay became famous for his role as the officious Chief Warden Mr Mackay, also appearing in a movie spin-off and the sequel series Going Straight.
• Other TV roles include an appearance in "The Return of the Cybernauts" for The Avengers, and he was a regular in Special Branch. There were also guest appearances in Some Mother's Do 'Ave 'Em, Dad's Army and roles in Z-Cars and Coronation Street. He hosted the UK version of children's series Fraggle Rock as the Captain.
• In 1983 he featured in the film Local Hero, appearing opposite Hollywood legend Burt Lancaster and future Doctor Peter Capaldi.
• He died, aged 64, in 1987, and is buried in East Sheen Cemetery. 
• Quinn has the first name Matthew in the novelisation by its writer Malcolm Hulke. His backstory was that he was the son of a famous scientist who bullied him into Physics when he really wanted to be a palaeontologist. He had been married but his wife had died in a car crash.