1812. A young prostitute named Mary leads a willing Redcoat out into the woods for some fun when he starts getting a little too fresh. She strikes him back and then scampers off further into the woods. She notices a bright light and a weird buzzing sound and goes to investigate. The Redcoat catches up to her, aims his pistol at her and fires.
Our gang pulls up to a dig site. They find an old alien thingamajig along with a skeleton that has a big hole in the chest cavity. We are shown a lingering shot of a short-haired blonde woman watching the crew. She looks a lot like Mary.
Poor Tosh feels like no one understands her and goes out for a drink. The same blonde woman from earlier shows up and rattles off a considerable amount of information about Tosh, introducing herself as Mary, a "scavenger": basically one of several people like Torchwood who collect alien objects but aren't nearly as organized. She offers Tosh a pendant that allows her to hear peoples' thoughts. Tosh says she'll show it to everyone else, but Mary is convinced she won't.
Naturally, Tosh doesn't, and we get a nice day of Tosh hearing everyone else's thoughts, including learning about Gwen and Owen's new affair, and Ianto hurting inside.
She meets Mary again and they discuss the powers of the pendant, which leads to them having sex. Mary suggests going out in public to be able to use the pendant better. Tosh does so and ends up thwarting a divorced man from committing premeditated Murder-Suicide, but still feels like she's being invasive after hearing more thoughts from her coworkers.
Tosh and Mary start dating. Tosh tells Mary that she'll give up the pendant to them, but Mary is rather insistent that she doesn't. She reveals herself as a telepathic alien who escaped from her homeworld and that the device Torchwood found is a transporter that can get her back home. She refuses Torchwood getting involved, as she believes they'll lock her up and study her.
It turns out to be a clever bit of manipulation, as Mary eventually lets Tosh convince her to take her into Torchwood to recover the transporter. Jack shows up to let Tosh know the truth: Mary didn't come to Earth alone in that transporter, she was sent here with a guard, whom she killed. She possessed the real Mary's body back in 1812 and plucked the heart out of the Redcoat, something she continued to do for years. She holds Tosh hostage in exchange for the transporter, which Jack gives to her, with the coordinates set for the centre of the sun. Tosh is horrified, but Jack quips that it's not that bad: the sun's probably not even hot, seeing as it's night.
- A Mind Is a Terrible Thing to Read: Tosh reads the mind of each of her co-workers and finds herself disgusted by their inner selfishness. The fact she cannot read Jack's mind only adds to the mystery about him.
- Beat Still, My Heart: Right through the chest cavity, Mola Ram style.
- Berserk Button: The British soldier hits the prostitute Mary after she compares herself to the Virgin Mary. She dryly notes that her client for the evening must be religious.
- Dirty Mind-Reading: Mostly between Gwen and Owen.
- Evil Sounds Deep: How Mary tips Tosh off that she's an alien.Put. The phone. Down.
- Even Evil Has Standards: Owen finds out that there are some things even the occultic circles won't do."I started looking into devil worship and stuff from that era [the 1800s], see if there's anything about plucking out hearts, and would you believe it, there's nothing! They ate eyeballs, they drank blood, they had sex with animals, but they did not pluck out each other's hearts, because obviously that would have been weird."
- Hearing Voices: The pendant makes you hear them all.
- Humans Are Bastards: Mary feels that Torchwood will lock her up and study her if she reveals herself to them. She's more afraid her crimes will be found out.
- Hurl It into the Sun: Or transport Mary there. End result's the same.
- I Am a Humanitarian: Mary needs to eat hearts to sustain her human husk.
- I Have to Go Iron My Dog: To get away from Owen, Gwen and their thoughts about their torrid affair, Tosh says, "I think my desk is on fire."
- Literary Allusion Title: The expression "Greeks bearing gifts" is from Virgil's The Aeneid.
- A Mind Is a Terrible Thing to Read: Tosh develops telepathy. She races home hurt and angry after hearing the thoughts of her co-workers (such as Gwen's commentary on her outfit and Owen's dismissiveness of her sentence turning into a ramble), although Mary assures her that they do like her and she's picking up on things beneath the conscious level that they're not even aware they're thinking. On the other hand, it does help her stop a man from killing his ex-wife and kid (and himself).
- At the same time, Jack is an utter blank to her, resulting in a Nothing Is Scarier situation. However, during the episode's climax, it's revealed that he may have suspected something and deliberately blocked out his mind, only letting carefully-selected thoughts slip to let Tosh know what to do. Given his past as a time agent, this could be part of his training, or it could be a side-effect of how the Bad Wolf changed him.
- No-Sell: When Tosh tried to read Jack, he seemed to be able to sense it and stopped the pendant from entering his mind but didn't ask Tosh about it.
- Out-of-Character Moment: Jack seems to have a problem with his transgender friend Vanessa, comparing her situation to Tosh hiding her telepathy and referring to her with male pronouns and the name Vincent when describing her transition. This does not gel with his (and 51st century people in general's) previous portrayals as being very open-minded and above the 21st century's various prejudices regarding gender.
- Pater Familicide: A divorced man attempts Murder-Suicide by pulling a gun on his ex-wife and son in their home. Fortunately, Tosh overhears his thoughts in the street, follows him and knocks him out from behind with a golf club before he can pull the trigger.Mary: They should make an action figure of you.
- Power Perversion Potential: And yes, Tosh and Mary use the pendant to think kinky thoughts to each other.
- These Are Things Man Was Not Meant to Know: Pretty much said word for word by Jack at the close.
- Whole-Plot Reference: To the Buffy the Vampire Slayer episode "Earshot", where Buffy gains telepathic powers, suffers from A Mind Is a Terrible Thing to Read, and uses them to prevent a murder.