Well, looks like last episode's rift opening did actually have some lingering effects. People and things from different time periods are popping up all over the world, causing the usual complications: Roman soldiers in the lock-up, bubonic plague spreading and virulent.
The gang, minus Jack, all start hallucinating. Tosh's dead mother warns her that something's coming out of the darkness. Gwen sees a vision of Bilis from last episode apologising. Ianto's dead girlfriend tells him to open the rift. Owen sees Diane, and gets angry with Jack and storms out.
Jack and Gwen find Bilis and he explains he can walk through time as easily as one walks across a room. He escapes before Jack can bring him in, but catches Gwen alone so he can show her a vision of Rhys dead. Gwen brings Rhys to the Hub to keep him safe, but apparently this is just what Bilis needed to get in and stab him dead.
Owen returns and announces he's going to open the rift, and everyone but Jack is going right along with the plan. Owen kills Jack, not knowing that it's only temporary. Everyone but Gwen is appropriately shocked by this. Gwen gets everyone's retinal scans to open the rift, Jack wakes up (scaring the hell out of his employees) and they head outside to inspect their handiwork. They find Bilis rejoicing over the release of Abaddon, the Great Devourer. As it stalks Cardiff, people die beneath its shadow. The only solution? Send the one man who can't die. Jack's overwhelming life energy destroys Abaddon, and leaves Jack dead... for a few days. He comes back to life just as Gwen's kissing him goodbye. He gets a big hug from Tosh, kisses Ianto and lets Owen sob in his arms for a bit.
Everyone's back to relative normal (Rhys is alive again) and at least on speaking terms. As Gwen muses upon Jack's resistance to opening the rift, she asks what could tempt him to do it. Jack's only response is "the right kind of doctor". Suddenly, Jack's odd hand-in-a-jar starts beeping and a familiar whooshing sound is heard. Next thing anyone knows, Jack has vanished, to parts unknown.
- Artistic License Medicine: In reality, any doctor would recognize the symptoms of bubonic plague without having to be told by Owen. The episode gave the impression that it's a historical disease that's been eradicated, but that's not the case. It's still a relatively common disease in the developing world even today. There was an epidemic in India in 1994 and in Madagascar in 2017. It also occurs in western countries as a relatively rare side effect of the vaccine for it (typically given to people travelling to countries where it is still a problem), and in people working for organizations like WHO who travel to these same countries to help with outbreaks. The only difference is, in modern society it's preventable with improved sanitation and treatable with antibiotics. This trope is also subverted, in that the antibiotics named by Owen that he says they need to take immediately are the exact antibiotics used to treat yersinia pestis infection.
- As the Good Book Says...: Ianto opens the episode by quoting from the Book of Daniel.
- Berserk Button: Jack pushes Owen's and... HOLY CRAP.
- Big Bad: Abaddon. He racks up one of the highest body counts in all of the DW universe within seconds by simply lifting his shadow over people, like a curtain of death, and dozens of victims have their souls wrenched out of their bodies.
- Break the Cutie: Gwen's biggest break yet, after Rhys' death.
- Call-Back: While Owen goes through the secure safe in the Hub, he pulls out the knife paired with the Resurrection Gauntlet, as well as the quantum transducer.
"Son of the Great Beast, cast out before time, chained in rock and imprisoned beneath the rift."
- We've met the Beast before. Abaddon essentially is Beast Junior. Both were imprisoned, have unspeakable potential to inflict terror and death upon weak mortal creatures, and both seemingly met their demise in some incredible way that seemed to be definitive. Both also go on a rampage that cause an extreme loss of life and much senseless carnage, as would befit beings of ultimate evil.
- Crisis Point Hospital: Cardiff A&E finds itself facing this predicament after the Rift disgorges a woman from the 14th century into the middle of the hospital: she's carrying Bubonic Plague, and the disease quickly spreads to the staff and the patients. Thankfully, the hospital is still functioning well enough to have all forty victims quarantined and accessed only by doctors in HAZMAT suits... but it's made clear that it might not have been enough. Worse still, the Rift may spit out other disease carriers from across history, meaning that if the situation continues, Cardiff A&E will be completely overrun.
- Disney Death: Rhys is brutally slain by Bilis Manger, but when time reverts back to the way it was before the rift screwed it up, his death is undone.
- Easily Forgiven: The Fuck-Up 4 nearly destroy the world, suffer no consequences, and all get hugs and kisses from Jack. The guy they shot to nearly destroy the world. But they feel remorse for it, and Owen, the shooter, cries his eyes out when he learns Jack is okay. Sympathy wins them redemption in the end.
- Foreshadowing: In the beginning of the episode; after Ianto finishes reading from the Book of Daniel, starts another book with the words; "Abaddon; the great devourer, who will leave the world in shadows".
- Karma Houdini: Bilis.
- Not to mention every Torchwood member other than Jack. Especially Owen. But in Owen's case, he felt horrible about what he did.
- Nice Job Breaking It, Hero!: The Torchwood crew, sans Jack, open the rift, releasing Abaddon. Then Jack himself, after giving his whole team a "The Reason You Suck" Speech, getting decked by Gwen once he pissed her off, then shot in the head when he pissed off Owen.
- Our Time Travel Is Different: Bilis doesn't need fancy watches or police boxes.
- Precision F-Strike: Gwen drops a giant one after Jack makes an armor piercing statement and she responds with an armor piercing punch.
- Relationship Upgrade: Jack and Ianto share their first on-screen kiss (that isn't meant as CPR).
- Sealed Evil in a Can: Abaddon.
- Set Right What Once Went Wrong: Everyone besides Jack thinks this is the best idea after they all either lose loved ones or have visions of them.
- "The Reason You Suck" Speech: Jack delivers one to each of his teammates as they are about to open the rift.You're a united front now? Toshiko, the poor girl who'll screw any passing alien that gives her a pendant? Owen, so strong he gets in a cage with a Weevil, desperate to be mauled. Or Ianto, hiding his cyber-girlfriend in the basement. Your three comrades here pumped bullets into her, remember?
- Time Crash: Of the "people from all over time are popping up" variety.
- Too Dumb to Live: According to the Expanded Universe, some humongous dumbshits thought it was a good idea to pull out their mobiles and record the hell demon Abaddon instead of running as it and its soul-thieving shadow came after them, and dropped dead with their phones still clasped in their lifeless hands.
- Wham Episode: Owen kills Jack and Jack resurrects. The whole team now learns he is immortal. Rhys is killed (he gets better) and Gwen hits the Despair Event Horizon. Then a huge demon appears and starts murdering Cardiff with its own shadow! Jack almost dies for good and takes weeks to resurrect rather than moments, by which time he's gone pale like a stiff, making it seem even more unlikely that he'd come back to life, and more shocking when he actually does. But worst of all- the villain gets away.
- What Happened to the Mouse?: Bilis Manger eerily disappears after his purpose of summoning Abaddon is served. The Expanded Universe reveals he's vanished to parts unknown to cause disasters anew.
- What the Hell, Hero?: Jack and The Team exchange this with one and other. The Team on Jack for trying to stop them and Jack to the team for nearly destroying Cardiff.