It's another morning in Madrid and people are going through their daily lives. Salesman Sergio is calling a client to tell them about his latest wares, vagrant Israel is kicked out by the police for sleeping on the streets again, gambling addict Trini asks the grocer to put today's expenses on her bill, and young Elena is telling her friend on the phone about the date she's going on with a guy she met online. When Elena's phone runs out of battery, she decides to enter a bar to have a coffee and ask if employee Sátur may have a charger he can lend her.
Right behind her, a coughing sick man also enters the bar and rushes to the bathroom, making owner Amparo angry because people are always using her bar's toilet without buying anything. Israel suddenly barges in as well because he knows Amparo will feed him for free, and his constant, loudly quoting of the Bible is an annoyance for everyone there, including an inpatient bank clerk, a streetcleaner, and former cop Andrés; but it doesn't seem to bother Nacho because he has his headphones on. Sergio and Trini come into the bar, and Trini is ready to spend all the money she has left on the bar's slot machine.
When the bank clerk gets tired of waiting for his breakfast, he decides to leave without eating, but as soon as he steps outside, he's shot. Everyone in the streets runs away and all the people in the bar panic, although it takes Nacho a moment to catch on to what's going on because he didn't hear the gunshot. There's no signal inside the bar, meaning they can't call the police, so the streetcleaner decides to go out anyway.
Unfortunately, while he's checking on the bank clerk, he's shot as well. Israel laughs and continues to quote the Bible as the others panic and throw themselves on the floor just in case. In fact, Israel wants to leave since he has church today, but Amparo convinces him to stay by offering him more food and promising to talk to the priest later.
Trini carefully reaches for the remote and turns on the tv, but as she surfs through the channels, the group notices something very weird: nobody is talking about the deaths that just happened in the middle of the streets of Madrid, which is incredibly suspicious. While everyone argues about it, Trini looks outside and finds something even more suspicious: the bodies are gone, and there isn't even a drop of blood left. They don't understand why somebody came by to pick up the bodies but didn't check on them, and the group tries to keep itself busy by watching tv or chatting while waiting for help.
Sátur begins throwing crazy theories around, wondering if this is a dream or if they've been abducted by aliens, or even the government. After Amparo slaps him to make him see sense, the group starts going over the facts. Elena thinks maybe the two guys were connected, but it doesn't sound likely for a streetcleaner and a bank clerk.
Sergio, on the other hand, realizes that maybe it's not a criminal who is doing the shooting - it's the police. They may've received a tip-off saying an important criminal is inside the bar, but they don't know who it is so they shoot anyone that comes out. If it's someone very dangerous like a terrorist carrying a bomb, they can't risk letting them out.
It would explain why the area has been evacuated and why the cops aren't bursting in to catch them. As everyone discusses this theory, Nacho decides to hide his bag before they find it suspicious, but he's caught red-handed. Sergio and Andrés hold Nacho while Sátur grabs the bag, but he doesn't dare to open it.
Amparo takes it from him and opens it herself, finding a bunch of clothes and a hard disk. Nacho swears it's just work files, but as another argument begins over what to do with it, Elena takes it, throws it on the floor, and repeatedly steps on it until it's destroyed. Then she calls everyone babies for obsessing over dumb theories.
However, Nacho is angry that he was found suspicious just because of his beard and because he ignored the shot, thus he points at Sergio's suitcase to make the same accusation. Amparo takes the suitcase and Sergio tries to get it back, causing to Sátur jump in to defend his employer and Sergio hits him instead. Startled, Andrés takes out a gun to make him stop, and everyone is so shocked that Israel takes the chance to steal the suitcase.
After quoting the Bible again, he opens it, only to reveal a bunch of lingerie - that's the product Sergio sells. At that moment, a weird noise comes from the bathroom: they had forgotten about the sick man. The door is locked, so Andrés shoots it to open it, and they find the man on the floor bent over the toiler with bleeding ears and a weird-looking syringe next to him.
Suddenly, another noise gets their attention, this time coming from the streets. It's a truck carrying special masked agents that ignore the group's cries for help and, instead, pile up tires outside the bar to then start a fire. This fire lets out a heavy, dark smoke that appears on tv.
The news anchor talks about a big fire in the middle of Madrid, so the group realizes this has been started by the government to cover up the killings. The sick man then comes out of the bathroom in a terrible condition, he drops his phone and tells them "don't touch me" before he falls to the floor and dies. Nacho grabs the man's phone and by looking at the pictures, they find out he belonged to the military and used to work in Africa.
The pictures also show a group of men wearing hazmat suits. Now everything it's clear: this man has brought a deadly disease with him. That's why the area has been evacuated and anyone from the bar is shot: most likely, all of them are already infected, and the government is covering it all up.
Thinking they're going to die, everyone goes back to trying to keep themselves busy while waiting, and Israel prepares the sick man for funeral prayers. Elena and Nacho have the sick man's phone, which only has ten percent battery left, and they decide to try to find a signal. Nacho manages to do it by standing on a chair near a higher part of the bar ceiling, so he calls a coworker to explain the tv is lying.
Thinking Nacho's not being urgent enough, Sátur takes the phone from him and begins desperately yelling for help, which makes the coworker think it's a prank and hang up. Nacho doesn't think there's enough battery left for another call and the two men begin fighting over the phone until the chair breaks and they fall, pushing everyone back in the process. This makes Trini hit the slot machine and hit jackpot, getting it to expel a bunch of coins that Israel begins picking up.
Andrés wants a turn with the phone next, but Amparo warns him not to touch it because it used to belong to the sick man. In fact, Amparo wants everyone that touched the sick man to stay away from her. Andrés and Sergio agree with her, thinking precautions should be taken, so they run away from the group that did touch him to hide with Amparo behind the counter.
Elena thinks this is ridiculous because they've been together for hours now, and they've all touched each other, but the trio is firm on their decision. In fact, Andrés threatens them with his gun to make them go down the storeroom and take the sick man's body with them. Nacho doesn't want to go but changes his mind when Andrés shoots the slot machine to show how serious he's being.
Isreal is taking his sweet time as well, too busy quoting the Bible, thus Amparo convinces him to go by giving him two bottles of alcohol. Inside the dirty old storeroom, the group chats to pass the time, but Trini is claustrophobic and starts to panic. She climbs the stairs and begins hitting the door to no avail, and in her desperate flailing, she accidentally hits a box of bottles, breaking them.
Nacho notices that there isn't a pool of liquid forming, which means there must be a drain that they manage to find after moving some stuff aside. After they remove the lid, they discover it's connected to the sewers and not very deep, so Israel volunteers to go down there. He takes off his clothes and leaves his bag of coins behind before covering his body with oil, then he attempts to go down the drain.
No matter how hard the others help him by pushing though, the space is too narrow for Israel and now he's stuck. Suddenly, they hear noises coming from upstairs: it seems a group of people has entered the bar and is shooting Amparo, Andrés, and Sergio. Then, they notice the temperature getting warmer and smoke coming from the door: a fire has been started inside the bar to disinfect it.
At this rate, they'll suffocate soon, so Elena, Nacho, and Sátur put their strength together to get Israel out of the drain in order to allow air to come in from the sewers. Trini's going through another anxiety attack and tries to open the door, getting her hands burnt in the process. They cover her burns with oil and wrap her hands with toilet paper while waiting for things to calm down.
Once they don't hear any more noises upstairs, Nacho opens the door with a broom and finds the burnt bar but no sign of the bodies. The door has been taped out by the agents, meaning they can't see what's going on inside. The group decides to come out of the storeroom and Nacho finds Andrés' gun, so he hides it in his pants even if the warm metal burns his skin.
Trini wants to go outside and ask for help, but Nacho reminds her that revealing their presence will only get them killed. None of them feel sick, which makes Nacho think it's just a matter of staying hidden for a few days until the incident is forgotten - after all, there's plenty to eat and drink in the storeroom. A sudden noise startles everyone, but there's nothing to worry about - it's just the sick man's phone, which is getting a bunch of messages.
Elena checks them out and discovers a friend is checking on the guy to see if he's ok. It seems the man had had a fever for days, he was also aware that he was being followed. He entered the bar looking for a bathroom in order to inject himself in secret because he had stolen some sort of experimental serum.
It didn't work on this man, but to be fair, he had been sick for a while. In contrast, nobody in the group has symptoms yet, so there's a chance it may work for them. At that moment, the phone begins ringing - the person from the text is now calling.
Nacho isn't sure if they should answer because it may be a trap, and it takes him such a long time to decide that the phone's battery runs out. Sátur runs upstairs to see if he can find a charger that fits when Elena remembers something: one of the messages said something about "four doses left". The group checks the body and finds nothing, which gets them to rush to the bathroom next.
Israel gets there first, finds the box with the other four syringes, and begins singing when he realizes he has power over the group now. There are only four doses for five people, and while the group discusses how to proceed, Israel injects himself with one, suspecting that they'd vote out the hobo. Nacho takes out the gun but doesn't shoot because Elena points out they'll be heard by the cops outside; instead, he jumps on Israel to beat him up.
Israel manages to overpower him and gains control of the gun, so when Sátur tries to retrieve the syringes, Israel hits him and the box falls into the storeroom. Trini rushes downstairs and picks it up, but because of her bandaged hands, she lacks coordination and accidentally drops the box in the sewers. Someone thinner needs to go through the hole, meaning their only option is Elena.
After taking off her clothes and covering her body with oil, Elena gets into the hole. Trying to go down hurts her thighs and makes her bleed, but the group keeps pushing until she goes through and falls into the dirty water. It doesn't take her long to recover the box of syringes, but she refuses to tie it to the wire Nacho is lowering because she knows they'll use them all and leave her with nothing.
Elena wants to be better than them so she won't be using one on herself either, but if the others want to have a proper discussion about this, they'll have to come down too. Elena goes exploring while the group uses a piece of pipe to make the hole bigger. After a few turns, Elena finds a storm drain and takes a look after hiding the syringes in a hole in the wall.
On the streets, special agents and cops are still surrounding the area and taking care of the bodies they retrieved from the bar. Then, Elena goes back to the storeroom hole, where she finds the men have already come through and are now helping Trini, whose flailing makes everyone fall into the water. Sátur and Trini get out alright, but Nacho takes the chance to jump on Israel to try to recover the gun.
A fight ensues underwater, and after a few shots are fired, Nacho comes out victorious, saying it was Israel that did the shooting and disappeared in the water after Nacho took the gun from him. The group thinks Nacho killed Israel, who is acting more and more violent by the second. Tired of everyone acting crazy, Elena requests Nacho to throw away the gun if he wants her to take them to the syringes.
Instead of doing as she says, Nacho threatens to kill Sátur - now Elena has no choice but to take them to the wall from earlier. On their way there, Trini makes use of the bag with coins she took from Israel earlier and drops coins on the ground so they can find their way back. When they reach a dark tunnel, Trini cries out, pretending that Sátur is pushing her when it's actually her pushing him into the water.
Then she pretends to try to help him out when in truth, she's grabbing his head and keeping him down to drown him. Nacho fires a shot to get some light and sees what Trini is doing, so he quickly jumps into the water to help Sátur out. Then, they move to a tunnel with more light while keeping Trini at gunpoint, but Nacho doesn't dare to shoot her.
Trini confesses she doesn't like to be seen and she grabs the gun, taking it around the corner in order to end things herself. The remaining trio finds the syringes and divides them among them, but before they can do anything, they hear the sound of coins being tossed. They go to see what's going on and find Trini's body with coins over her eyes.
This turns out to be a trap, because while they're distracted by Trini, Israel approaches them from behind and kills Sátur. Then, he chases after Elena and Nacho, who run through the tunnels until they find a set of stairs that can take them outside. As they climb up, Elena trips and loses her syringe, and Nacho is grabbed by Israel.
Seeing as there's no escape for him, Nacho gives Elena his syringe and lets go of the stairs, making both men fall and die. Crying, Elena injects herself, then pushes the manhole lid at the end of the stairs until she manages to move it and get out. She finds herself on the other side of the containment zone, so there are people everyone staring at the state of her looks.
A man tries to ask if she's alright and a woman gives her a jacket, but Elena doesn't pay attention, she just wanders away with a dazed look on her face. She's incredibly lost in her own mind and doesn't notice that she walks by the guy she was supposed to have a date with - he even calls her name, but Elena just keeps moving forward.
