A man calling himself Mr Ashcroft has come to speak with Mickey, an elderly dame who once worked as a waitress in a nightclub called Bianca’s. Bianca’s was a bolthole for radicals and intellectuals, where the persecuted could drink the night away while they were entertained by Bianca’s singing voice. The whole club was bugged so Bianca could listen to what people were saying about her, and now the tapes are all that’s left of the nightclub. Mickey invites Mr Ashcroft to share a drink with her while they listen to the story unspool...

Back in the day, the tomboyish young Mickey was one of the few waitresses who could keep up with the pace of life at Bianca’s. The club’s owner, Henry, organised the special taxis which escorted the clientele to and from the club; strictly teetotal himself, Henry lurked in the shadows and watched to ensure that the revels didn’t get out of hand. And Bianca was the star of the show; every night at midnight she sang her heart out on stage, accompanied by the pianist Heinrich. Invariably wrung dry by her performance, Bianca would then retreat to a table in the shadows, where the clientele would pay tribute to her.

On this particular night, her visitor is a newcomer to the club, and he’s thus rather taken aback when she refers to him by name as the Doctor. He is even more taken aback when he sees another newcomer entering the club, a drunken and bedraggled woman being escorted by the thugs who patrol the streets outside Bianca’s entrance. Henry has made a special arrangement with Corporal Sturmer to avoid trouble, and he thus has Mickey escort Sturmer and his men to their exclusive booth and serve them free drinks. Henry himself remains to deal with the newcomer -- the infamous Iris Wildthyme.

Iris perches herself on a barstool and orders the house special, an unlabelled tequila-like drink. She claims to have wandered into Bianca’s at random, but Henry doesn’t buy that claim. The only way into Bianca’s is by special taxi, yet now two strangers have appeared as if from nowhere, and Henry is determined to learn how. The Doctor arrives, as if on cue, and drags Iris away, demanding to know what she’s doing here in 1930s Berlin. Much to his surprise, she doesn’t moon over him as she normally does; in fact, she claims that she doesn’t really fancy him in his current body. Unsure whether to be pleased or not, the Doctor changes the subject and berates Iris for her heavy drinking -- but she tells him that she needs to drink, in order to hear the voices in her head...

At this point, the damaged, decades-old tape grinds to a halt. Mr Ashcroft loads another spool onto the player, and hears Bianca apparently talking to herself, mumbling into a glass of tequila and claiming that “they” will soon find the harmony they seek. He then finds another tape containing the rest of the conversation between the Doctor and Iris, whom Mickey compares to worms in some ways -- they are slippery, hard to pin down, and able to regenerate damage their bodies. On the tape, Iris claims to have erased herself from the Time Lords’ database, which is why they don’t know about her; and Mickey points out that, likewise, if anything were to happen to these tapes, there would be no evidence that Bianca’s ever existed at all.

As the Doctor and Iris argue, the matter of the Doctor’s trial comes up; irritated, the Doctor points out that at least the Time Lords have actually heard of him, prompting Iris’ claim to have erased herself from their records. Iris’ increasingly drunken behaviour attracts Henry’s attention, but she assures him that she’s perfectly fine, and then falls over. Henry asks the Doctor and Mickey to help move Iris into the office so she won’t disturb the other clients, and as they do so, Iris mumbles confused warnings to the Doctor, claiming that this nightclub is not all it seems.

Once Iris is settled down on the chaise-lounge, the Doctor decides to have a chat with Bianca about this odd club. Before he can do so, Henry demands to know how the Doctor really found the club, and reveals that the Doctor was spotted emerging from a strange blue box near the lavatories, slipping out of the club and then letting himself back in through the front so as to avoid attention. The Doctor is surprised to learn that he was seen amidst all the shadows, but refuses to explain how he got the blue box into the club without being seen. Henry claims to respect his clients’ privacy, but secretly vows to learn the Doctor’s secret...

Mickey is fascinated by what she’s hearing, as she’d missed all of these little secrets the first time around; she was concentrating on her work at the time, trying to ignore the weird things she could sense lurking in the shadows, worming their way into the lives of the people at the club. On the tape, her younger self becomes unnerved by the weird echoes to Iris’ snoring and decides to use the hidden microphones to listen to the other clientele instead. Mr Ashcroft becomes interested when the tape picks up a conversation between Allis and Ballis, two scientists discussing dimensional instabilities. But the elderly Mickey informs him that their conversation isn’t the important sound on the tape; even the young Mickey could hear something at the time, faint whispers in the background like shadows of the conversation...

Bianca enters the office, and is disgusted to find the sleeping Iris -- but she’s even more furious when she discovers that Iris has apparently stolen several bottles of the house special. She slaps Iris awake to accuse her of theft, but as they argue, the Doctor arrives and demands answers of them both, having sensed that there is indeed something strange about this nightclub. He thus decides to get Iris back to her bus to sleep off her bender somewhere out of the way while he investigates. They have some trouble getting past Corporal Sturmer, who wishes to amuse his men by allowing them to “escort” Iris away from the club; fortunately, Henry intervenes at the right moment, reminding Sturmer that he and his men have yet to enjoy Bianca’s singing. The Doctor takes the opportunity to usher Iris out, ignoring Mickey’s vain attempts to give him a token for the taxi ride home. Henry then retreats to the office, where his private phone is ringing -- and the rasping, hollow voices on the other end inform him that he can use both the Doctor and Iris to bring their plans forward...

Mickey notes that Mr Ashcroft doesn’t seem surprised by the revelation that Bianca’s club was a portal to other worlds, with entrances on many different worlds. At the time, of course, Mickey had no idea that the club was not in Berlin, as Henry always arranged for a taxi to take her home. As later events would prove, even Henry didn’t fully understand the nature of the club’s dimensional portals -- but he fully intended to...

Since the Doctor has no token for the taxi, its driver unhelpfully leaves the Doctor and Iris stranded in the void outside until Bianca’s opens again the next evening. Irritated, and upset with himself for failing to work out what was going on earlier, the Doctor orders Iris to fetch scientific equipment from his TARDIS so he can learn the truth about Bianca’s, while he tries to warn Bianca herself about the dangers of building a solid structure in a dimensional nexus point. However, Bianca is already quite aware that the nexus point is unstable, which is why she’s opened the doors of her club to the people who can help her. The Doctor finally sees and recognises Allis and Ballis, noted interdimensional physicists; unfortunately, they’re noted mainly for accidentally destroying an entire star system in a failed experiment. Despite the Doctor’s dire predictions of disaster, however, Bianca warmly welcomes him to her club -- and he finds himself surprisingly uncomfortable in her presence.

As Iris fumbles through the shadows near the lavatories, looking for the TARDIS, Henry finds the door ajar and shuts it, trapping Iris with the shadows -- which brush her skin and whisper in her ear. At the last moment, Mickey hears Iris shouting and opens the door, dispelling the shadows; however, she insists that Iris leave before Henry catches them here, claiming that this area is out of bounds. Shaken by her experience, Iris returns to the nightclub floor and begins to chug a bottle of the house special, much to the Doctor’s irritation. Meanwhile, Henry speaks with the shadows, who gleefully inform him that they’re growing stronger; and with Bianca, who puts Henry firmly in his place when he refers to “our” opening night. Henry may be the one who fixes the dimensional conduits and keeps the nightclub stable, but Bianca is the star of the show. But she’s unaware that Henry has his own agenda...

The Doctor decides to speak with Allis and Ballis about the dangers of the dimensional nexus, but when he joins their conversation, a chance remark about his TARDIS leads to a startling revelation. According to Allis and Ballis, the club itself is a TARDIS, or what’s left of one. Its shielding has been modified, so that within the dimensional nexus it is both everywhere and nowhere at once -- which is the only reason the Doctor didn’t inadvertently Time Ram it when he materialised here in his own TARDIS. Now very deeply disturbed, the Doctor heads for Bianca’s table and waits for her to return, determined to make her see the dangers.

Iris finishes off an entire bottle of the house special and makes her way backstage to Bianca’s private dressing rooms, where she’s surprised to find that at least one of Bianca’s dresses is exactly like one of her own. In fact, it is her own... Mickey tries to get Iris to leave, but Iris insists that she can hear voices -- and Mickey realises that she too can hear whispering. Iris opens up one of Bianca’s powder compacts to reveal a worm inside, and Mickey realises that the worm is trying to speak to them. Henry arrives and catches Iris, but she stands up to him and demands to know why he lets Bianca boss him around. Henry admits that Bianca has recently become patronising and disrespectful, and Iris suggests that he get rid of her and hire a new singer. Unfortunately, when she mentions that she used to sing herself, albeit in a different body, this gives Henry an idea. Before Iris realises what she’s gotten herself into, Henry is insisting that she take Bianca’s place in the cabaret, and he won’t take no for an answer.

Bianca returns to her table to find the Doctor waiting to confront her, but she already knows the danger posed by her club’s presence in the dimensional nexus. However, she insists that things are the same everywhere; wherever the world is about to unravel, one will find song and dance and a cabaret. The Doctor concedes her point, and when Bianca offers him a drink and a sympathetic ear, he admits that he was deeply hurt when his people put him on trial; even though it was all a set-up, he still feels that nobody is ever grateful for all he does for the Universe. Realising that the Doctor is lonely, Bianca questions his feelings for Iris, and the Doctor admits that he’s too much of a loner to give Iris what she thinks she wants from him. He finds it oddly easy to confide in Bianca, and although he thinks he hears whispers echoing in her voice, she dismisses them, claiming that he’s looking for a mystery where there is none in order to justify his aloofness. Before the Doctor quite realises what’s happening, Bianca insists that they dance, and sweeps him off his feet.

Realising that Iris has fallen under some sort of spell, the Doctor has Mickey pull out the microphone lead while he apologetically hits Iris, knocking her out. The clientele return to normal, and Bianca soothes them by offering a free round of the house special. The bartender has been injured, and Allis and Ballis step in to pour the drinks. The Doctor theorises that some evil intelligence hijacked Iris’s song, projecting hostile intentions through the sonic harmonies -- but Mickey claims not to have heard anything unusual. The Doctor also remains concerned about Sturmer and his troops, whose shadows are definitely out of synch with their actual bodies.

The Doctor then speaks to Iris, who is recovering quickly backstage; fortunately, she finds her surroundings surprisingly easy to relax in. Some time ago, Iris found herself on the planet where Bianca’s house special is distilled, and she stole a crate of the liquor -- but ever since, she’s been hearing two sets of voices in her head, each saying something different. This is why she’s been drinking so much of the house special; it helps to make the voices clearer. She passes out, happy to realise that the Doctor is genuinely concerned for her.

Henry receives a phone call from his shadowy allies, who are pleased with the results of the riot; the “anti faction” has been given a taste of power, and the “pro faction” now knows the strength of their opposition. Soon the factions will make their move, and Henry must be ready to act. Henry thus sets off to find the Doctor, who is chatting with the exhausted Allis and Ballis. In gratitude for their help, Bianca has offered them lodgings for the night. Despite their assurances, the Doctor still believes that the dimensional nexus is unstable, and when Henry casually presses him for a solution, the Doctor offers a possible technological band-aid. Henry actually understands his explanation, indicating that he’s more knowledgeable than he’s been letting on -- and the Doctor realises that he’s starting to hear strange, shadowy echoes in Allis’ voice...

Iris breaks into Bianca’s dressing room to steal the compact with the worm in it, and checks one of her stolen bottles of Bianca’s house special to find that, as she’d suspected, there’s a worm floating at the bottom of the bottle. Iris came here because the voices in her head had claimed that Bianca was treating the worms as slaves and abusing their powers, but when Iris chugs enough of the house special to make out what the worms are saying to her and to each other, she soon learns that she’s been manipulated...

The tape with the exposition is worn and torn, and Mickey fills in some of the gaps for Mr Ashcroft as best she understands them. It seems that the worms evolved on a world affected by the dimensional instability of the nexus point, and that they developed the ability to foresee their own future. Disgusted by the thought of evolving beyond their sleek simplicity into hairy and complex creatures, the worms divided into two factions with different plans to deal with the situation. The “pro faction” formed an alliance with Bianca, intending to focus their powers through her singing voice and freeze the Universe in a single perfect moment, thus ensuring that nothing ever changed again. But the “anti faction”, the ones which had lied to Iris, preferred to hold the Universe in a moment of utter violence in which everyone lived only for the moment with no regard for the future, severing all ties with all other living things and thus never progressing or changing. Iris now realised too late that the two factions were equally bad, but by that point she was too drunk to resist their commands. And all the while, as Mickey now knows, Henry and his allies had yet another agenda...

Looking for Iris, the Doctor instead finds Bianca, who offers him a drink. She hasn’t forgiven Henry for using Iris against her, and the Doctor sympathises; in fact, he realises he’s more than sympathetic. Bianca’s presence is having some strange effect on him, and he’s finding it difficult to concentrate on the real problem, the tiny wormholes which are opening throughout the club, connecting it to all corners of the Universe. Bianca insists that one strong voice can maintain stability even in this maelstrom, but the Doctor knows that she’s describing a benevolent dictatorship, which is just what he’s fought against all his life. However, Bianca suggests that the Doctor believes in his own right to pass judgement on others -- which is why he was so hurt when the Time Lords did exactly the same to him. He claims that he wants to help others, so why fight universal harmony? Doesn’t his scepticism just mean that he can’t bring himself to trust, and therefore to love?

Mickey shakes Iris awaken to prepare for the cabaret, but Iris notes that Mickey seems somewhat shaken herself. Mickey admits that she’s been paying attention to her surroundings for the first time following the riot, and she’s spooked by what she sees. Whenever Henry lets people into the club, they are joined by shadows which are not their own; Allis and Ballis’s voices have acquired strange whispering echoes; and the Doctor seems obsessed with Bianca. In fact, he’s behaving as if he’s in love. This news snaps Iris sober instantly, and she remembers some of what the worms told her -- enough to remember that she and Bianca are on opposite sides.

The Doctor and Bianca hear Iris shouting angrily and enter the office to confront her -- and to Iris’ shock, the Doctor admits that he does feel something for Bianca. Somehow, he feels as though they’ve known each other for much more than a day. Iris collapses in tears and accuses Bianca of using the worms to twist the Doctor’s mind, but Bianca in turn accuses Iris of consorting with the evil anti faction -- and orders the Doctor to prove his love for her by killing Iris for the sake of the Universe. To Iris’ horror, the Doctor takes the pistol which Bianca provides, and drags the screaming Iris into the dressing room as Bianca laughs.

While listening to events unfold on the tapes, Mickey points out that Bianca is going to a lot of trouble over Iris when she could just throw her out of the club. Somehow, Mickey feels that Bianca really did care for the Doctor in her own way -- just as Iris did...

At the last moment, Henry and Mickey enter and interrupt the Doctor, who shoots the chaise-lounge and collapses in pain. The worms redouble their efforts to control both the Doctor and Iris, who realise they need to get out of the club in order to think clearly. Henry summons a taxi, but as he opens its door, the Doctor and Iris catch a glimpse of a shadow slithering out of the taxi and into the club; this is how Henry is bringing them here.

The taxi driver transports the Doctor and Iris to Berlin, where the shimmering daylight makes everything seem oddly flat -- or perhaps the dimensional instability is spreading out from the entrance to the nightclub. Iris then spots Bianca strolling down the street, and forces her into the taxi to explain herself. Bianca mockingly sits on her hands as if being kidnapped, but agrees to give the Doctor and Iris all the explanations they want, over coffee. However, Iris is horrified when Bianca finally reveals the truth. Bianca is an embodiment of the dark sides of Iris’ personality, and she has lured her past self into her affairs in order to steal her remaining regenerations. The Doctor examines the gun which Bianca gave him and finds a distillation chamber built into its handle; had he shot Iris, the gun would have drawn in her remaining regenerations, for Bianca to absorb later.

The Doctor is naturally outraged, as Iris has once again plagiarised his life; however, when the stricken Iris storms back to the taxi, the Doctor does accompany her, realising just what she’s going through. As he comforts her, however, he realises that the taxi driver is racing through the streets at an alarming rate, and when he examines the seat where Bianca was sitting on her hands, he discovers that she’s hidden another distillation chamber under the upholstery. The dimensional circuits have been sabotaged, and soon the hypnotised taxi driver will have built up enough speed to ensure that any crash will be fatal to all concerned. However, the Doctor shorts out the dimensional circuits with Iris’ earrings, forcing the taxi to jump back into the void outside Bianca’s.

The driver pilots the Doctor and Iris back to the club, which Iris realises must be the remains of her own TARDIS, her double-decker bus; this is why it seemed so comfortable earlier. The club is now surrounded by shadow, and inside, the Doctor and Iris find that the shadows have possessed most of the clientele. The Doctor realises too late that this is why Henry wanted to stabilise the dimensional nexus -- so the shadows could remain stable within it as well. He and Iris must learn the shadows’ agenda, which means that Iris must start drinking the house special again. The worms’ psychic frequency must be attuned to this brand of alcohol, which means that everyone who drinks it becomes susceptible to their control.

Mickey can no longer deny that something weird is going on at the club, but when she takes her concerns to Henry, she discovers that he’s responsible for it all. According to Henry, the shadows are the disembodied spirits of the creatures which the worms would have evolved into; their potential existence has been stolen from them, just as Bianca has always mocked and run down Henry’s own potential. Thus, when the shadows contacted him, Henry agreed to help them acquire corporeal form and live the lives they were cheated of. Panic-stricken, Mickey goes to Allis and Ballis for help, but to no avail. Henry has drained all of the knowledge he needs from them; Allis is a pale shadow of his former self, and there’s no sign of Ballis at all. The regular clientele sit joylessly in their seats, waiting solemnly as Henry prepares for the final cabaret.

By now, the worms have become aware of the shadows’ existence, and Bianca is horrified when the pro and anti factions reveal that they’ve joined forces against the shadows. Iris falls under the worms’ thrall, and even Bianca finds herself unable to resist the combined force of both factions. Now she and Iris will sing on stage together, united against their common enemy. As they take the stage, the Doctor realises too late what’s happening; if Bianca and Iris sing in harmony, they will breach the dimensional nexus, and the shadows will spread throughout the Universe. Corporal Sturmer stops the Doctor from interfering, and Heinrich begins performing the showstopper, the one which will bring the house down. As Iris and Bianca sing in harmony, the voices of the worms echo throughout the cabaret, and the shadows come to life.

The Doctor finds the terrified Mickey, who tells him everything she’s learned and leads him to the controls in Henry’s office. The Doctor realises that Mickey is immune to the worms’ song because she never drinks the house special; however, everyone else in the club except Henry is now on the same psychic wavelength, and is amplifying the worms’ power and boosting it through the wormholes to reach every point in space and time. And since the shadows are the ghosts of what the worms could have been, they can hijack the same mental frequency and use it to possess the peoples of the Universe. Though the Doctor sympathises with the shadows, condemned to a twilight existence while still aware of what it was they’d lost, he will not allow them to take over the Universe.

The Doctor searches for the codium links which Henry had modified to stabilise the dimensional nexus, but Sturmer bursts in, under the shadows’ influence, and attacks him. In the course of the struggle, the room is wrecked and the Doctor finds the controls he’s been searching for. He apologetically hits Sturmer, knocking him out, but the rest of the club’s clientele attack. However, the Doctor then finds Ballis hiding in the office, and realises that if he isn’t dead after all, there’s still a chance to save the others who have been possessed. The Doctor thus orders Ballis to evacuate everyone to the cellar, while he takes Mickey to the TARDIS. It’s surrounded by shadows which are nearly corporeal enough to attack them, but when the Doctor opens the doors of the TARDIS, the light from the console room drives the shadows away.

Up in the cabaret, as Henry gloats triumphantly, Bianca tries to sing louder to drown him out -- but Iris stops singing, realising what she and Bianca are doing. The worms are losing the battle, their stunted potential twisted out of shape by the dark futures they tried to deny existence. Bianca insists that all the Universe sing in harmony, but Iris realises that this is just giving the shadows what they want. Iris thus joins the retreat to the cellar, dragging Bianca along with her even as the sobbing chanteuse insists that the show go on.

As Mickey reels in disbelief at the TARDIS’ interior, the Doctor thinks aloud; the shadows, obsessed with the need to exist, have no idea what to do with existence what they’ve got it, and they must be stopped before they spread chaos throughout the Universe. And the Doctor knows how to do so. The barricades which protect the club from the nexus point have been broken, and thus if the Doctor’s TARDIS tries to materialise within the nightclub again, the two TARDISes will Time Ram and the wormholes riddling the nexus point will collapse. In the cellar, Sturmer and Ballis are smashing the bottles of liquor, killing the worms within and breaking their link to Bianca’s clientele. The Doctor then attempts to materialise inside the cellar once again, and up in the cabaret, Henry realises the danger too late. The club is rocked by a tremendous explosion as the Doctor’s TARDIS Time Rams Bianca’s...