A woman called Beth wakes up to a burglary, blacks out and wakes up to find one of the thieves dead and the other seriously injured. She's taken in by Torchwood, who cautiously probe her until the alien inside her shows itself, removing a form of biological invincibility built into her body to do so. Beth's arm suddenly mutates into an organic interface, and she begins spouting an alien language, giving no information that would compromise the Sleepers' mission, who are from Cell 114.
There are a lot more aliens like Beth around who fully believe they're human. They'll be activated soon. Unfortunately, Beth's early awakening seems to stir them to action, whereupon several innocent people are sent to their deaths as former loved ones suddenly gore up people in positions of power, let their baby roll into oncoming traffic with the maternal side of their personality rubbed out, and carry out suicide attacks. Three Sleepers activate- two blow themselves up, hitting targets that cut off communications in Cardiff. The last Sleeper prepares to cause an even bigger boom by breaking into an old nuclear store, where he will begin launching and exploding the warheads. Owen pesters Tosh to contact Jack, but she can't get it through his noggin that the entire telephone network is down until Ianto ridicules him with every form of communication being cut off- even the tin cans with strings.
The end of the world is nigh, and it seems humanity has only a few moments left to live. Owen suggests they all have sex. "And I thought the end of the world couldn't get any worse", Ianto retorts. The aliens are thwarted in the end. The rogue Sleeper has his immunity to bullets removed like Beth's, and gets shot down. A lot more talkative and sadistic, the Sleeper eagerly blows himself up to keep Cell 114's activities from being compromised.
Tragically, Beth does not like the idea her sleeper agent programming will soon kick in and erase her humanity. She knows that putting her in cold storage will also fail, since her body was engineered to thwart such things. Instead, Beth forces Torchwood to pull a Suicide by Cop and lunges at Gwen with her Sleeper body's arm blade extended. Vulnerable to bullets with her defenses disabled from their experiments, Torchwood shoots Beth, breaking off her blade, and she perishes with her humanity intact. Gwen laments Beth's death, but Jack realizes she knew Torchwood would have ended up killing her soon enough and wanted to make it easier on them.
Stashing away Beth's broken blade, Jack wonders where the rest of Cell 114's Sleepers might be, as Gwen prepares to tie the knot with Rhys. For the meantime, Torchwood must keep on doing its job, ready if the Sleepers resurface.
- Aborted Arc/What Happened to the Mouse?: The last Sleeper implies that there are other cells active on the planet. To date, they have never appeared or even been mentioned again.
- Body Horror: The sleeper agents' arm blades aren't pleasant to look at.
- Coming and Going: Played for Laughs. Before the team is invariably blown up, Owen decides that if everyone's gonna die, it might as well be during a threesome with his teammates. Ianto finds that notion beyond disgusting. Owen's idea doesn't get off the ground floor.
- Deadpan Snarker: Ianto turns into one when faced with Owen's suggestion of having group sex before dying.Owen: Let's all have sex.Ianto: And I thought the end of the world couldn't get any worse.
- Dying as Yourself: Beth.
- Hollywood Exorcism: The Torchwood team's efforts to force the alien inside Beth to manifest have a strong technofantasy-infused resemblance to this.
- Manchurian Agent: Beth, and all of the other Cell 114 Sleepers, are programmed to blend in seamlessly with the dominant species of a planet. They are given false memories and false identities to make them believe they are human (or whichever species) but are always passively gathering information to transmit back to the invasion fleet. When the aliens have gathered enough information, they will eventually strike, though that still hasn't happened yet. Maybe the existence of Torchwood and the Doctor on Earth made them wisely decide against invasion?
- Mind Probe: Torchwood Three is in possession of (a particularly painful) one. note
- Pre-Climax Climax: Owen is clever enough to suggest an orgy when faced with impending death.Owen: And what if they can't stop it?Toshiko: They'll stop it.Owen: Yeah, but what if they can't?Ianto: Then it's all over.Owen: ...Let's all have sex.Ianto: (very deadpan) ...And I thought the end of the world couldn't get any worse.
- Suicide by Cop: Deciding that her life will eventually be erased by her programming anyway, she feigns that her sleeper personality is being reactivated and attacks Gwen, prompting Torchwood to shoot her dead.
- Tomato in the Mirror: Beth has Sleeper conditioning buried in her subconscious that will eventually activate and wipe out her humanity. She decides to stop that from happening by giving up her life in the end.
- What Measure Is a Non-Human?: The core dilemma of the episode. Without her sleeper conditioning, Beth acts, talks and thinks just like any ordinary human being. However, everything she is was merely programmed by her alien creators. And yet, she decides to die on her own terms, as a human.