Gaynor Mason (born George Staines on 13 February 1949) (Sara Stewart)is a pre-operative transsexual.

As a boy, Staines hates school, never feeling that he fits in, and never smiles in any of his school photographs. His favourite treats are his mother's flapjacks which he eats whilst playing old songs for her to sing, such as Cole Porter's "Don't Fence Me In".

As an adult, he leads a gang of vicious criminals in the 1970s and does not think twice about knee-capping his victims. He cuts off the left leg of a henchman named Charlie for talking about him.

In 1980, Staines stages his own death, and hires "Metal" Micky Dillon to identify the charred corpse of a tramp on whom Staines had planted his sovereign ring.

Staines flees to Spain for gender reassignment surgery. After receiving breast implants and cosmetic surgery to her face, she is blackmailed by her surgeons who demand more money or they will inform the authorities about her identity. She returns to Britain as a blonde woman, adopts the name Gaynor Mason, and sells cosmetics door-to-door.

In 1982, Gaynor becomes friends with Bryan and Marjorie Drake who live a couple of streets away from her childhood home. She gives their fourteen-year-old son, Peter, a football shirt and tells him that she might take him to a match someday.

Needing money to pay for the next phase of the gender reassignment surgery, Staines/Mason reverts to her former life of crime. Using her natural male voice and adopting Metal Mickey's modus operandi of wearing a mask of Prime Minister Margaret Thatcher to conceal her identity, Staines robs the Drakes on the morning of 8 November 1982,stealing approximately £1000 and some jewellery, including the necklace Marjorie was wearing. Bryan struggles to defend his family but is shoved by Staines and strikes his right temple on the table edge. The wound leaves him deaf for the rest of his life.

After robbing the Drakes, Staines visits her mother in the guise of Mason in order to bid her good-bye. Feeling sorry for her, Mason hides £500 of the stolen money in a tin of her flapjacks

After finding Staines' fingerprints at the Drakes' home, and believing that Mason is Staines' companion rather than Staines himself, DCI Gene Hunt offers Mason money to lure Staines to one of Staines' old haunts, the Peacock pub. That night, however, she encounters Peter Drake who recognises her necklace as the one stolen from around his mother's neck the day before. Fearing for his life when she chases him, Peter cracks Mason's skull with a brick, retrieves the necklace, and runs away mistakenly thinking he killed her.

Mason's gender and identity are revealed after she comes around in hospital. In attempting to escape, she takes down Hunt and DS Ray Carling before being kneed in the groin by DC Chris Skelton. She ultimately confesses in exchange for CID not telling her mother the truth and breaking her heart.

She discourages Carling from resigning from the police and enlisting in the Army, telling him, "I want to go to sleep at night knowing there's [sic] cops like you helping keep good people like my mum safe."

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