Gwen has been arguing with Rhys over her dangerous work, and Jack tells her that he wants Rhys out of harm's way so that Gwen will always have someone to go home to. The team finds an artefact in a back garden in Pontcanna, an insect chrysalis with alien writing that only shows up under ultraviolet light; they take it back to the Hub for analysis, but the chrysalis splits open and a monstrous insect emerges, knocking Jack unconscious, ripping Owen's face open, and mauling Gwen as it tries to escape from the Hub. Tosh lures it up to the Rift Manipulator and seals it in a bubble of slow time, but this is only a temporary measure -- and its only weak point appears to be the all-but-inaccessible soft palate in its mouth. Jack takes Gwen to hospital and calls Rhys, who blames Jack for Gwen's condition but does not interfere when Jack leaves to deal with another emergency. Ianto and the injured Owen have found a second chrysalis on a building site, and the insect has already hatched and slaughtered the construction workers. The insect grows to nine feet tall and begins wreaking havoc in the city centre, and Ianto, Jack and Owen try to stop it while Tosh works on translating the alien writing. Gwen awakens and checks herself out of hospital despite Rhys's protests, and, realising that he can't stop her from trying to help her teammates, he helps her back to the Hub. The second creature makes its way to Millennium Stadium and starts howling out a challenge, and a chance remark from Rhys causes Tosh to have a revelation: the creatures are opponents in some sort of battle, and may have been dumped on Earth so they wouldn't cause collateral damage on some other world. On Owen's suggestion, Tosh lowers the time dilation field and lets the first creature out of the Hub so the two insects can battle it out in the Millenium Stadium. Gwen insists upon seeing the battle for herself, and when she and Rhys arrive, one of the insects is distracted just long enough for the other to overpower and kill it. The victor then advances on the Torchwood operatives, bellowing out a challenge -- and Jack shoots it straight in its open mouth, piercing the soft palate and killing it. The alien bodies disappear, leaving Torchwood with the problem of explaining the trail of wreckage through the city centre; however, Rhys has come to understand that Gwen puts herself in harm's way in order to keep innocent victims out of it.

Torchwood investigates the brutal murder of Frank Jenkins, a low-level dealer in alien artefacts who may have fallen foul of a legendary criminal kingpin called Mr Glee. Owen and Tosh find a DVD addressed to Torchwood amongst Frank's possessions, and learn that Frank had acquired the Book of Jahi, an artefact capable of controlling Rift storms. Aware that he was out of his depth but unable to destroy the artefact, Frank hid it in his old flat in Cwmblaidd, a village about to be submerged beneath a new lake created as part of a hydroelectric project. While Tosh tries to learn how to operate the Book based on Frank's instructions on the DVD, Owen visits Frank's young trophy wife Kelly and tries to assure her that Torchwood is doing all it can to solve her husband's murder; however, he's unaware that Kelly is in league with Mr Glee, and informs her that Tosh is learning how to use the Book of Jahi. Tosh is thus kidnapped from her home by Mr Glee and his associates, Mr Lime and Mr Croker, who are revealed to be alien Blowfish. The frustrated but biologically challenged Owen remains at the Hub to monitor the others' progress while they try to rescue Tosh, who has been taken to Cwmblaidd to recover the Book. Kelly and the Blowfish take the book and blow up the stairs of the flat as they retreat, leaving Gwen and Jack trapped in the building with minutes to go before the village is flooded; however, Jack leaps out of the seventh-story window while holding Gwen, cushioning her body with his and then returning to life after the fall kills him. The Blowfish return to their limousine only to find that Ianto has sabotaged it, and sirens begin to sound, presaging the flood. The Blowfish order Tosh to use the Book to transport them all to safety, but instead she transports Kelly, the Blowfish, and their limo to the roof of a block of flats. The Torchwood operatives flee back to the SUV and escape as Cwmblaidd is submerged beneath the floodwaters. But back at the Hub, Ianto points out that being submerged underwater probably wouldn't be fatal to a fish...

Torchwood investigates the deaths of Rick and Craig, co-directors of Wilkins Advertising, who both spontaneously combusted while waiting in line to enter a new nightclub. The police reports indicate that they burned from the top down, and Ianto discovers that a new satellite appeared in geostationary orbit above Cardiff a few weeks ago. Gwen checks out recent deaths by fire in the Cardiff area, and discovers that a statistically significant number of the victims were advertising executives -- and the advertising company Southerland House has since scooped up their clients. Jack and Gwen investigate, and discover that the company's creative director, Peter Southerland, has an alien control device in his office, disguised as a work of modern art. Presumably, Southerland stumbled across it and discovered he could use it to eliminate his competition. Southerland catches them studying the device and pulls out a remote control from his pocket, and Jack and Gwen flee. Southerland chases them to the roof and operates his remote control, but as Jack had hoped, Southerland hadn't quite grasped that it takes microwave energy 16 seconds to travel between the satellite and the Earth. Jack reveals that he boosted the power from the microwave ray before Southerland caught him, and he and Gwen simply step out of the way, allowing the beam to burn down through the roof and destroy the control device eight storeys below. Now all Gwen has to do is stop Jack from throwing Southerland off the roof.

A dark figure walks out of a Rift storm, its shadow spreading through the streets and taking apart everything it touches -- architecture, animals, and people. Torchwood is alerted to the crisis as power losses spread across the city, and Jack, Gwen, and Ianto evacuate the Hub as darkness spreads across the plaza. Jack confronts the figure at the centre of the shadows, which identifies itself as Gordian; it is a World Eater, a swarm of nanobots designed as a weapon of war, and although it's only fallen through the Rift by accident it will still take apart the Earth within 24 hours. Jack sends Gwen to organise the evacuation of Cardiff, but Ianto insists upon staying by Jack's side; however, Ianto then tries to rescue a five-year-old boy named Tom, and they are both devoured by the shadows. Tom's grief-stricken mother Sheila tries to attack Gordian and is also devoured. However, Jack can tell that on some level, Gordian is lonely and knows nothing but destruction. He gives himself up to the swarm, and his immortal flesh renews itself as quickly as Gordian can devour him. Fascinated, Gordian pours all of itself into Jack, only to find itself trapped, endlessly devouring flesh that will never be entirely consumed. Jack and Gordian fuse into a single entity, which uses its power over the swarm to recreate everything and everyone that had been destroyed. Captain Jack Gordian then prepares to take its leave of the Earth, but Ianto begs it to leave Jack Harkness behind. Realising that it now has the power to create rather than destroy, Gordian restores the original Jack Harkness while retaining an echo of Jack's consciousness, and steps back into the Rift to go explore the Universe rather than simply devouring whatever it finds.

Synopsis coming soon.

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