SPOILERS FOR ALL CHAPTERS
This is a 1000-word summary of the events in The Last Door series. When possible, it's supported with text from the game.
There is another world. It contains the Final Truth, the First Language, and the Verb, which all might be different ways of referring to the “power of creation.” The other world is concealed behind a Veil. There is a region in the Veil called Zha’ilathal, which contains a portal that leads to the other world. The portal is called "The Last Door" and "The Last Threshold." It was created (or at least used) by ancient beings.
A being resides in the Veil. It is known as the Custodian, the Bird, and the Eye of the Bird. It might also be the Simurg, a creature from Persian mythology that is sometimes known as the Bird King. If a person in the Veil tries to approach Zha’ilathal, the Custodian will attack them.
Once a person reaches Zha’ilathal, the Custodian is no longer a threat. However, Zha’ilathal has dangers of its own. People in Zha’ilathal sometimes leave behind shadows that contain memories. If you peer into one of these shadows, you see one of those person’s memories. If you peer into your own shadow, you see one of your own memories, and you go insane and physically transform into a monster. Some people know how to peer into our world from Zha'ilathal.
In general, the other world is very well protected. However, there is a gap in its protection. If a person experiences “primal terror,” there is a chance that they will enter the Veil. If that happens, they can enter Zha’ilathal without encountering the Custodian.
Many cultures have myths about the Veil and the Custodian. However, not many people know about the “primal terror” method for reaching Zha’ilathal. There are a few exceptions. A medieval scholar named Raymundus Lully was apparently aware of it. The residents of Éilís Mór seem to have used it frequently.
The story of The Last Door essentially begins with Anthony's father. He traveled the world, collecting information about the Veil. He learned about the Last Door and the Custodian, but he apparently did not discover the “primal terror” method.
Around 1870, when Anthony was a teenager, his father died and left Anthony all of his research. Anthony used his father's notes to create a serum that would cause a recipient to enter the Veil. Anthony was a member of a science and philosophy club at his boarding school. Around 1876, he and the other members of the club injected themselves with the serum and entered the Veil for a few moments. They saw the Custodian, who also saw them. It seems that they weren’t attacked, but they were nevertheless haunted by the image of the Custodian’s birdlike eye.
After graduating, Anthony and his friends (Devitt, Hugo, and Alexandre) continued to research the Veil. They formed a secret society called the Playwright and recruited many new members. One recruit was Captain Skidd, who had a strange experience during the First Boer War in 1881. Based on his story, the Playwright suspected that he had entered the Veil and encountered the Custodian, but that he had been able to defend himself and a companion from harm.
Skidd led the Playwright on an expedition into the Veil. However, when the Custodian attacked, Skidd could not protect them. Some people were killed, while others experienced memory loss. Devitt fell into a coma. In the aftermath of the attack, Skidd became a drug addict and Hugo quit the Playwright. It’s possible that some of the survivors eventually committed suicide.
Meanwhile, a man named Professor Adam Wright learned about the “primal terror” method. He got in touch with the Playwright, who assisted him in testing the method. Alexandre recruited Hugo to take part in the test. In 1885, Hugo used Wright's method to enter the Veil. He bypassed the Custodian and reached Zha’ilathal. Unfortunately, no one realized that the shadows of Zha’ilathal were dangerous. Hugo peered into his own shadow and was transformed. The Playwright concluded (incorrectly) that Wright’s methods were flawed.
A few years later, in 1887, Anthony and Alexandre discovered Raymundus Lully’s research, which included the formula for a serum that induces primal terror. Alexandre injected himself with the serum. He entered a trance and apparently took up permanent residence in Zha’ilathal.
In 1891, Anthony went mad and hanged himself. Before his suicide, he sent Devitt a letter that reawakened some of his memories. The first season was mostly devoted to Devitt’s investigation into his own past. He returned to his old boarding school and was almost killed. Eventually, he found Alexandre’s mansion. Alexandre was still in a trance, but Devitt was able to awaken him. He persuaded Alexandre to inject him with serum. Devitt and Alexandre entered the Veil and set off for the Last Door.
In the second season, Wakefield and Kaufmann continued their search for Devitt. They tracked down Captain Skidd and Professor Wright. In 1893, Wakefield found the monster that had once been Hugo. After searching Wright’s study, they learned about Éilís Mór. Shortly thereafter, Kaufmann died of an unknown illness.
Wakefield traveled to Éilís Mór, where he experienced primal terror and entered the Veil. He found Devitt, who led him to Zha’ilathal. Devitt told Wakefield to cross the Last Door and meet him in the other world. However, as Wakefield approached the Last Door, Alexandre warned him that Devitt planned to close the Door.
The player can choose whether or not Wakefield goes through the Last Door. If he goes through the Door, he meets Devitt again. Wakefield remains in the other world and closes the Last Door while Devitt flees to London. If Wakefield does not go through the Door, he returns to London, where he speculates that Devitt has closed the Last Door.
- Alexandre: "Yes, Jeremiah gathered us all under the same rule. 'Videte ne quis sciat.' See that no one knows. We knew of the Final Truth, which lay beyond the Threshold. This is what the Playwright was committed to finding. This was Jeremiah's obsession. The First Language, which is said to grant the power of creation." (Chapter 8)
Devitt: "I had stood there, on the beach, staring up at the terrifying heights of the vertiginous Mount Qaf, where the Verb is said to lie." (Chapter 8)
- Alexandre: "Look now to the forest in the valley, to the old tower. From the last tree in the distance to the stars in the sky, and even the stones beneath our feet are just silhouettes that hide the truth from our poor senses. Ancient shadows that hang over the Veil that hides the world. As if it were the curtain of a theatre, the Veil separates the truth from the lie." (Chapter 4)
Alexandre: "You must find the door, as I did. The door that gives passage through the Veil." (Chapter 4)
Note on Alexandre's bed: "The Veil is something we sense in our innermost being incessantly. In vain do we waste our lives, craving to tear through. Zha'ilathal is the curtain behind which the great wings beat. Inside its ancient mist inhabit the shadows of those who left." (Chapter 4)
Member of the Playwright: "In this place, the ancient shadows created by human reasoning tremble in sheer terror. Its name is Zha'ilathal, the last curtain." (Chapter 8)
Member of the Playwright: "These ruins, built by beings long forgotten, grant access to the Last Threshold." (Chapter 8)
Alexandre: "The Other World protects itself. It conceals itself within a Veil... and it reacts violently when that Veil is disturbed." (Chapter 8)
- Anthony: "My father discovered several ancient myths pertaining to the Veil. They come from a variety of cultures and hence take many different forms. But they all say something similar about what resides near the Threshold. An ancient being that sleeps within the fog, protecting the Door from intruders. A vengeful Custodian… Those tales… they all say that if an intruder ventured too close to the Door, and was seen by what sleeps in the fog... It would pursue the intruders and destroy them, wherever they might hide. There would be few ways to protect themselves from its rage." (Chapter 8)
- Alexandre: "We needed a way to circumvent the inexorable gaze of the Bird. I found Captain Skidd, who had met the Bird and lived. We decided to use him in a test. It was a catastrophe. We eventually found the survivors, but their memories were... incomplete. Jeremiah had fared the worst. He had been left devoid of any memories that were related to our efforts." (Chapter 8)
- Ernest: "The Eye of the Bird saw us, it remembers us, it looks for us, it calls us from its dark nest, from its abominable lair." (Chapter 2)
- Shadowbook reader: "Simurg... Simurg... Ahh, yes, The Bird King." (Chapter 3)
See also The Simurg in religion and folklore
- Alexandre: "In some of Zha'ilathal's mirrors you see the Truth leaking into our world... and in others, you see yourself." (Chapter 8)
Sign in Zha'ilathal: "Peering into one's own truth is forbidden. Were the snake and the bird to meet, ultimate madness would take inhuman form." (Chapter 8)
Alexandre: "Hugo came here long before the rest of us. But he made a terrible mistake. He peered into his own truth... and he was transformed." (Chapter 8)
- Wright (presumably): "The trigger is the mind itself. The emotion known as terror. The primal fear that still survives in the depths of our mind, from the times humans were mere beasts. That which allows us to open a physical passage beyond the Veil of rational thought. Primal terror is the key that we will use to open the Last Door." (Chapter 6)
Alexandre: "He [Wright] is eccentric indeed, but I think his thesis may be proven correct. If so, we might have found a way of reaching the Threshold without attracting the attention of the Custodian. A shortcut, you might say. The problem is in the method itself. It has some… unusual requirements. And we would need a man of great sensitivity, who knows the peril of reaching the Door…" (Chapter 8)
See also Wright's log second part
- Letter from Anthony (July 1887): "My epiphany with the treatise of alchemy was not accidental. When examining the text closer I have come to the conclusion that for a time, Lully Raymundus sought the same thing as we did. In his account he describes a formula that he calls hoopoe - yes, like the legendary bird -. It closely resembles the serum with which we have worked so far, except for minor differences." (Chapter 4)
Alexandre: "Anthony and I miraculously came across a formula that had lain forgotten for centuries." (Chapter 8)
Alexandre: "We will use the serum to induce primal terror in a controlled environment." (Chapter 8)
Previously on: "He [Devitt] discovered his friend [Alexandre] had dosed himself with a new serum, leaving a catatonic body behind. This new drug was capable of transporting the mind permanently to the Veil and beyond." (Chapter 5)
- Previously on: "He [Wakefield] discovers the island inhabitants hold a terrible secret: they instill primordial terror in ritual subjects for them to cross the Door" (Chapter 8)
- Note in Alexandre's lab: "This and no other is the function of the serum we manufactured at the boarding school when we were young. It is something that we didn't understand by that time: to accompany the mind to the proscenium of the big theater, and there, help us to look behind the curtain that separates the world of men from and the land of truth." (Chapter 4)
Anthony: "At any rate, my serum was a failure. We got but a glimpse of what exists out there." (Chapter 8)
Ernest: "We opened that which should not be opened. In doing so, we shorn The Veil that separated our world from His. In seeking vision we were ourselves seen by the Eye of the Bird." (Chapter 2)
Alexandre: "After our experiment at school, we realized that the path of the ancient ones was watched by a fearsome guardian." (Chapter 8)
- Devitt: "There can be no doubt that the Captain survived an encounter before. He even kept a companion from harm." (Chapter 8)
See also Majuba Hill
- Conghill: "The last I heard from fellow veterans, he [Skidd] had lost himself to a frenzy of alcohol, opium and bad company." (Chapter 5)
- Hugo: "What brings you [Alexandre] here, anyway? It has been years since we have heard from you. I thought our old cause had long been forgotten." (Chapter 8)
- Devitt (examining Anthony's study): "A few press cuttings pinned to the wall: The Illustrated London News. 1887 - Judge kills himself under strange circumstances. The Daily Telegraph. 1888 - Earl found dead floating in the Thames. The Times. 1889 - Famous actor found bled to death in his hotel room." (Chapter 1)
- Alexandre: "We will succeed where Wright failed." (Chapter 8)
- Alexandre: "It may be for the best. Our research is likely to take some time. If he [Devitt] truly has amnesia, his condition will protect him until we are ready." (Chapter 8)
- Letter from Kaufmann (1893): "The doctors were unable to determine the cause of my sudden illness, nor have they found a cure. I have not much time left." (Chapter 7)
Alexandre: "I am truly sorry about your friend. Sometimes terrible fates befall the companions of Travelers." (Chapter 8)
- Alexandre: "When Jeremiah reached me, he did not remember everything. He had changed. He told me that he was going to put an end to all of this. He still means to acquire the First Language. But he wants to use it to ruin our work! He has already crossed the Threshold... Once he learns the Final Truth, none of this will ever have existed: the Order, the Door, or ourselves! You must stop him, Doctor. You must stop him before the Curtain closes forever!" (Chapter 8)
- Devitt: "He [Wakefield] said nothing, but it was not necessary. He had come to take my place, to sacrifice himself. He stayed behind and closed the Door after giving me the chance to escape. His reasons I will never know." (Chapter 8)
- Wakefield: "He [Devitt] had crossed the Threshold, leaving the Veil through the red curtain of truth, and forever closed the Last Door that had led to those horrors." (Chapter 8)