Trilby's Notes is a game in the Chzo Mythos series. It was the third made, but the second chronologically.
The game takes place four years after 5 Days a Stranger. Trilby, although confident John DeFoe is at rest, has become paranoid nonetheless and is eventually apprehended by the police, who offer him a job as a paranormal investigator as part of the Special Talent Project, a secret government agency. An author is encouraged to fictionalize Trilby, to make people forget he was ever real. Trilby later hears that Simone Taylor, a fellow survivor from the DeFoe Manor incident has fallen into depression and alcoholism, prompting a visit, but he instead discovers her murdered corpse. He then tells Jim, another survivor, to go into hiding. Deciding her death is related to the DeFoe incident, Trilby decides to do research on John to find a way to stop him once and for all.
He discovers that the wooden idol containing John DeFoe's soul has been passing through the hands of various dealers and is about to be put up for sale at the Clanbronwyn Hotel in Wales. He travels there in the guise of an antique scout looking for good deals for a rich client; when he arrives though, he discoveres that another STP operative, Agent Lenkmann, has been dispatched there to monitor him. He begins to inexplicably shift between this world and a nightmarish “dark world,” where a demon initially known only as the Tall Man keeps trying to kill him. Graffiti written in blood on the walls seems to refer to the strange figure, while a diary found next to a dead body suggests that the Tall Man is controlled by a higher power.
Over time, Trilby learns about the nature of the “dark world.” It is an alternate dimension called the World of Magick, in a realm ruled by a pain elemental named Chzo. A cult called the Order of the Blessed Agonies worships Chzo as a god, and seeks to bring him to this world. The Order knows the Tall Man as the "Prince", Chzo's highest servant: he was originally a 1st century BCE druid named Cabadath who attempted to summon Chzo to defeat the Roman forces that were invading the area. Instead, Chzo drew Cabadath into the World Of Magick. To punish him for his arrogance, Chzo imprisoned his soul in a tree and subjected it to slow agonies, driving him insane and turning him into the Prince. On the 28th of July each year, the day when the boundary between the worlds is weakened and Chzo can look upon the Scientific Realm, the Prince is given leave to roam free and take his revenge on all those who abuse the wood of his soul tree - that is, those who carve, burn, cut or otherwise damage the wood.
In hopes of bringing Chzo into this world (the "World of Technology"), the Order seeks to destroy all three aspects of John DeFoe (referred to by the Order as the "Bridgekeeper"), his mind, body and soul. As an individual born in the World of Technology who was killed by a magickal relic, DeFoe's obliteration would create a bridge allowing easy passage between the two worlds. Trilby had already destroyed his body in 5 Days a Stranger and his soul is contained within the African idol from DeFoe Manor (which will be destroyed in 7 Days a Skeptic.) Trilby is able to see the history behind the idol through flashbacks; the wood used for it came from Cabadath's soul tree, which was first felled by a Norseman, and centuries later used to build "The Unicorn Inn" and all its furnishings. The wood used to build the Unicorn was later used as material for keys for a harpsichord. Jack Frehorn, a man obsessed with the occult, later purchased this harpsichord and out of fear of the Prince formed the Order of Blessed Agonies; a masochistic cult devoted to fulfill the prophecies of Chzo. The harpsichord was then destroyed and made into a crate for the O'Malley Shipping Company. An African man eventually creates an idol out of wood from this crate, only to be killed by the Prince. Sir DeFoe then found the idol on one of his trips to Africa.
Trilby eventually finds the stump of Cabadath's soul tree near the hotel and identifies it as the center of the world-shifts; Lenkmann arrives and reveals himself as a member of the Order. He then proceeds to stab Trilby to subdue him and attempts to use him as a sacrifice to the Prince to allow him to manifest in the World of Technology. Lenkman is quoted as saying "I present you with 3 agonies, Body, Mind and Soul." He is refering to Trilby's wound, Siobhan's loss of the profesor, and Lenkmans many tourturings of the mind. He also could be talking about Tribly. The Body being his wound, the Soul being the loss of Simone, and the Mind having spent time in DeFoe Manor and Clanbrownwyn Island. But Trilby wills himself to death before the demon can be summoned. The Prince mortally wounds the agent in anger, and drags his soul into the Ethereal Realm.
Shortly after, Trilby is revived through mysterious means (not explained until 6 Days a Sacrifice), and takes the idol. Knowing he cannot merely destroy it, he closes the game pondering how to dispose of it safely. In the post-credits epilogue, the Prince and Lenkmann, now a "Puppet" used by the Prince to communicate, present the bloodstained waistcoat of Trilby to the Order of Blessed Agonies, thus continuing the fulfillment of the Prophecy of Chzo