It is 1943. In a tavern in Southern France, a young woman waits for someone, while Nazi soldiers celebrate. A man arrives and sits in front of her. The girl presents herself: she is a young Lola Mendieta, and mentions she likes "mincemeat" to the man, William Martin. Before they can do anything, an SS officer arrives, and Lola gives the other man (who speaks with a marked Andalusian accent even though he is English) documentation, and between her and the tavern owner they distract the Nazis so that William Martin can escape - but Lola is captured.
In 2017, Lola Mendieta is dying - presumably of the same cancer that took the lives of her Darrow partners - and is meeting with Salvador, who wants to ask her about the Soviet agent's murder, but she does not know anyting, although she offers him a deal: if he stops Darrow before they begin traveling, she will revive and give him the full Book of Doors - although Salvador is not keen on the deal.
In Elena's home, her and Alonso are having a small argument over Alonso's sullen manner before he is told to go to the Ministry - where he is told they must go save the young Lola Mendieta before she's sent to a concentration camp, where she will be forced to reveal what she knows about Operation Mincemeat - and for once, it is Pacino who tells the story of how the British fooled Adolf Hitlernote , as The Man Who Never Was was one of his favorite films. For this mission, they will be accompanied by Ernesto, who is not a novice in this kind of mission.
The setup is easy: they will stop the van where Lola is being taken, and Ernesto will tell them to hand Lola over. However, when one of the false soldiers nervously lights up a cigarrette and one of the German soldiers in the van asks for another, it turns out the false soldier does not know German, which makes the Germans realize it is a trap - just as more Germans are coming from the other side. A shoot out ensues, killing most of the Ministry workers. Ernesto and Lola try to run to the runaway car driven by Pacino, but then Ernesto gets shot and Lola stops to attempt to help him. Alonso, Amelia and Pacino must run away, leaving Ernesto and Lola behind to be captured by the Germans, who take them to the Gurs internment camp.
With the mission a total loss, the patrol is told to go to Punta Umbría, and contact Lola's British contact to ensure Operation Mincemeat goes forward, while other plans are made to rescue Ernesto and Lola - although Salvador prepares for the eventuality of Lola's death, which would mean all of her missions would completely change.
Ernesto and Lola bond over their life, as Lola tells Ernesto about her past. At the same time, Salvador speaks with Angustias, and reveals something: in the original timeline, Lola Mendieta was not involved with Operation Mincemeat - which means history has changed because of the Ministry. Salvador mentions this must be the Butterfly of Doom... before exclaiming "Fucking butterfly!".
In Punta Umbría, Huelva, the trio meets with William Martin, revealing to him that they come from Lola. With the new situation resolved, William sends a message to England, telling them he can restart Operation Mincemeat, but he's told it has been aborted. William becomes angry, mentioning how he's lost everything because of the war and now only lives to take revenge on the Nazis but Pacino suggests something: organizing the entire operation themselves, calling it "Operation Meatballs". Confidence renewed, William seeks the help of a fellow Brit-like Andalusian, who aids them in collecting all the documents they need to fake the agent.
In Gurs, both Ernesto and Lola are being heavily tortured, but neither speaks up, although Lola indicates she is scared she might end up revealing everything if this continues. At night, they are visited by a priest, who Lola scornfully tells off before going back to sleep. The priest, though, is a Ministry agent, who tells Ernesto he must kill Lola if it appears she might reveal anything.
In Punta Umbría, the team must provide further documentation in the form of the photograph of the agent's "girlfriend": Amelia becomes said girlfriend, and the entire group enjoys a day in the beach, playing football. However, they are still several ingredients, including love letters and a corpse. The love letters are taken care of by William and Amelia, the latter starting to cry as she pours her love for Julián. Meanwhile, Alonso - after some prodding by Pacino - tells him he's trying to get Elena pregnant but can't, and Pacino replies that Elena is probably taking contraceptive pills, another thing from the future that surprises Alonso: Pacino suggests he talk about it with her, but warns him to take the issue respecting Elena and her rights.
That night, the British government attempts to communicate with William, warning him that Mincemeat has restarted, but his telegraph machine is broken and doesn't receive the message.
That night, in Gurs, Lola confesses she's afraid of dying, and it is implied she might end up telling all about Operation Mincemeat. Ernesto considers killing her in her sleep, but in the end he cannot go through it.
With everything ready for "Operation Meatballs", they are only missing the corpse, but, unfortunately, none of those in the Punta Umbría's morgue fits with what they need. While everybody sleeps, William decides there is only one thing to do: he takes the documents, dresses as a British officer and goes to the sea to drown himself. Alonso realizes what has happened and rushes to stop William, but William replies he does not mind dying if his Heroic Sacrifice will lead to the Allied victory, giving Alonso his medallion.
In the morning, William's friend comes in a rush, only to learn what he has done, and he reveals to the patrol that Mincemeat went forward without their knowledge, so now they must get William's body back before he is found. Pacino fixes William's telegraph, and they are given the news: the sub that was expected to put the corpse in the water was sunk before it could fulfill its mission, so now William Martin is, indeed, the Man Who Never Was. A short while after, William's friend meets with the German consul in Huelva and ensures he cannot bring William's corpse to Berlin, instead being buried in the tomb that now bears the man's true name, instead of his fictitious identity - and Pacino requests Isabel, William's friend's young daughter, to bring fresh flowers, which she does. Pacino says that, at least, they have managed to pull the wool over Hitler's eyes - and, indeed, the dictator (whom we already saw a while back) swallows it hook, line and sinker.
In Gurs, it looks like the Germans are done with Lola and Ernesto, so they take them out of their cell to execute them. Hands behind their back and their eyes covered, Lola has the time to Face Death with Dignity by insulting the German soldiers. Before the execution is carried through, though, the Germans are shot in the back: The Cavalry, led by Salvador, has arrived just in the nick of time. Salvador then decides to recruit young Lola, ten years before he did in the original timeline - or ten years later. It depends on your point of view. However, when he comes to visit old Lola, it turns out she finally succumbed to cancer - while her friend bitterly denounces Salvador's actions. So, for Salvador, now rests the issue of wondering whether his actions will change anything at all.
In the Ministry, Irene brings Salvador a photograph: it's the previous episode's builder/killer. Irene tells Salvador the man was a Ministry agent back in the fifties, someone that had gone missing during a mission and declared dead (not the first time, as Lola Mendieta got out of the way by doing this), which means a lot of the past has changed: is this the only "missing" agent that may actually turn up alive and well later? Salvador also has a request for Irene: he wants her to be in charge of young Lola Mendieta's training in the Ministry.
In the end, Pacino - who had been mystified by something - realizes where he knew William Martin's name from (bringing the book "The Man Who Never Was"). Pacino and Amelia discuss whether their actions were always meant to happen or if it was their changing the past that prompted their time traveling, but Alonso asks to stop talking about the issue, which he'd rather not think about, since it's been on his mind ever since he started to work at the Ministry. Pacino wonders if Isabel did as he asked... and not only has she done so, but her family helps her with this (Truth in Television, by the way (in Spanish)).