Mary is the main antagonist of the Torchwood episode "Greeks Bearing Gifts". She is an Arcateenian fugitive in the form of a human woman who forms a relationship with Torchwood agent Toshiko Sato in order to regain her transporter.
She is portrayed by Daniela Denby-Ashe.
Mary was a female Arcateenian imprisoned for unknown offences. In 1812 (Earth years) she killed her guard and used his transporter to escape from prison, arriving in a forest on Earth. She encountered a nearby prostitute and possessed her. She then immediately ran into a soldier who had been chasing the prostitute, who shot her. She responded by ripping out his heart and eating it. She left the transporter behind in the forest, figuring she could always go back and get it if she wanted to leave. It was buried when the city of Cardiff was built.
Over the next couple of centuries Mary remained on Earth, eating human hearts to sustain herself. However, in 2006 the transporter was unearthed by Torchwood Three alongside the body of the soldier. Mary detected this and returned to Cardiff in order to retrieve it. She approached Torchwood Three operative Toshiko Sato in a pub and asked her about Torchwood, having gleaned its existence through mind-reading. Claiming to be a collector of alien artefacts, she gave Tosh a mind-reading pendant and got her to use it to read her mind, revealing a desire to kiss her. Tosh was shocked and embarrassed, but Mary convinced her to keep the pendant.
Later after reading the inner thoughts of the rest of the team, Tosh returned home in distress to find Mary waiting there. She admitted to Mary that the others pitied her, and Mary replied that thoughts were complicated. She convinced Tosh to use the pendant on her, leading to both of them thinking about sex together. They passionately kissed and slept together. Afterwards Tosh shared her feelings for co-worker Owen Harper with Mary.
In a later meeting Mary asked Tosh to use the pendant to read Torchwood Three's commander Jack Harkness for information on the transporter. However as Jack had previously died multiple times the pendant didn't work on him. After this Tosh wanted to hand the pendant in to the team, but Mary convinced her not to by revealing her true form and claiming that Torchwood would just imprison her if she handed in the pendant. Instead she asked Tosh to steal the transporter so she could go home.
However, when Tosh and Mary arrived they found Jack with the transporter. Jack explained that he had figured out it was for a prisoner and a guard. Mary admitted she was an escaped prisoner and that she had killed several people to eat their hearts. When the team refused to hand over the transporter she took Tosh hostage at knifepoint, using her telepathic powers to turn the team against each other by revealing their secrets. Eventually Jack seemingly gave in and threw her the transporter. However Jack had previously rigged its coordinates and when Mary caught it she was immediately teleported into the sun and killed.