Roots: Fairy / Fey legends.
There are references to the Cottingley Fairy photographs, Arthur Conan-Doyle, and Harry Houdini. "Lord of the Dance" plays in the background during the playground attack.
Goofs: Houdini didn't believe the Cottingley Fairies photographs were genuine. [Owen is mistaken, and Gwen had forgotten the details from her school essay.]
If some of Jack's men killed the fairies' chosen one why did all of them die? And why wasn't Jack attacked? Also, the other fairy attacks are fairly noisy, yet in this one all that's heardis a fluttering of wings.
The fairies don't show up on the cell CCTV, but do show up on both the Cottingley Fairies photographs and Estelle's photographs. Also, they're invisible when attacking at the marketplace or Estelle's house but visible when attacking the barbeque. What determines when they can be seen and when they can't?
Why do Torchwood get called in to the suffocation in the prison cell? And, in that scene, why do they have Tosh (the IT specialist) examine the corpse rather than Owen (the doctor)?
Dialogue Triumphs: jACK: "Think dangerous, think something you can only half see like a glimpse, like something out of the corner of your eye with a touch of myth, a touch of the spirit world, a touch of reality, all jumbled together. Old moments and memories that are frozen in amongst it. Like debris spinning around a ringed planet. Tossing, turning, whirling. Then backwards and forwards through time."
Continuity: Jack says that tfhe fairies are from the dawn of time, they are worse than alien because they are a dangerous part of our own world that we can only half see. They play tricks with the weather. They can fill somebody's mouth with flower petals – suffocating them to death. They play games, tormenting and then killing their victims to protect their chosen ones. They were all children once, taken from different moments in time going back millennia. They are part of the lost lands. They want the next Chosen One. It is not explained how he knows any of this.
At school Gwen wrote an essay on the Cottingley glass plate photos. Conan Doyle and Houdini believed them, but when the girls who took them were old ladies they admitted they were fakes.
Roundstone wood has an odd history – in ancient times it was considered unlucky to walk in there or even to collect timber, even the Romans stayed clear of it. It appears to be part of the Lost Lands, and a chosen one of the fairies can see it even when there's not much left in the real world.
Links: Jack thinks the fairies might be part Mara (Kinda/Snakedance).
Location: Various locations around Cardiff (Roundstone wood, Plymouth Road, Coed y Cymru Primary School, Old Forest Road, the Hub, an unidentified marketplace). Given that there's a barbeque party it's between mid spring and mid autumn.
The Bottom Line: "One needs to have the patience of a saint and the blind faith of a prophet. But for me the long wait has been worthwhile." It's felt a long time coming but Torchwood finally has a good episode, and it's one that delivers on the promise of telling the kind of adult stories that can't easily be told in a family show. The fairies are a horrific and truly credible threat to the regulars as well as the guest cast, and the whole thing holds together really well.