The weekend passes uneventfully. On Monday, the investigators receive word from Scotland Yard that the documents for the Roby murder case are now available. When they arrive they find Inspector Taylor waiting to interview them about the recent events in East Anglia, but it rapidly becomes clear that he does not expect that either case will be satisfactorily solved and is simply going through the motions.

The Roby case files are in fact available but contain little that is new. The most significant point is the whistle that was heard just before the attack. Although there is no mention in the case summary several servants report this in the interview transcripts, and a whistle that was found in Alexander's room is included with the evidence. Its form is familiar - similar to the one in the investigators' possession and the other that they spotted in Clare Melford, near what was left of Dick Blair. There was also a routine inquiry made about the Roby estate: 45% of the family fortune went to Grahame and 20% to Alexander, with a further 15% held in trust for Alexander should he marry. The remaining 20% was left to Georgina, and was divided between the surviving brothers according to the existing scheme. As next of kin, Graham has taken charge of Alexander's money, believing himself better placed to manage it than the family solicitor.

Tuesday night is the night of the full moon, and the investigators have plans to follow Bacon when he leaves his house. They meet Vincent Tuck in pub near King's Cross and make their final plans. Georgina and Ludwig are unarmed; Alex and Aubrey are both carrying revolvers, which Tuck warns them not to use in anything but a dire emergency. He hands round police whistles, with which they may be able to summon help if there are officers on the beat nearby. When the pub closes, Tuck and the investigators take up station at the end of Bacon's street. The night is clear and bitterly cold, and the watcher placed there by Tuck is glad to give up his post.

It is past midnight when Bacon leaves the house. He heads west towards King's Cross and the Regent's Canal, with the investigators following at a safe distance. Reaching a bridge over the canal, he slips though a gap in the fence and scrambles down to the towpath. The investigators follow and find themselves on a wharf where warehouses, many of them disused, front onto the canal. Ahead of them Bacon seems to be searching for something, walking carefully along the icy towpath. He quickly finds what he is looking for: a figure sleeping in a sheltered doorway. He walks over and shouts something in a high-pitched voice. The words resonate, seeming to come from all around. The tramp screams and tries to rise to his feet. Still speaking, Bacon grabs him by the throat and holds him off the ground with one hand.

The investigators make themselves known with a medley of shouts and whistle-blasts. Bacon throws the body of the tramp against the wall, where it shatters into dust and fragments. He turns to face the investigators. "Coombs!", he shouts, "Damn you, Coombs! Where are you? You're needed!"

Tuck and Aubrey rush him, while Alex and Ludwig advance more carefully. Georgina stays by the bridge and and tries to call the police. Tuck is the first on the scene, but Bacon makes a quick fluid gesture with one hand. Suddenly, Tuck is flailing his arms, trying to dislodge the crawling snakes that no one else can see. Bacon breaks open the warehouse door with his shoulder and rushes inside. Aubrey follows, but quickly finds that his artistic constitution makes him a poor sprinter. Ludwig stops to examine the body of the tramp. It is so dry as to be effectively mummifies, and has broken into pieces.

The next few minutes are confused. Tuck manages to collect himself and follows Aubrey and Alex into the warehouse, while Georgina remains by the bridge and Ludwig scrambles back up to street level and tries to find a front entrance. The warehouse itself is long-disused; many of the glass panels in the roof are gone and the floor is strewn with rubble and lumps of rusted iron.

Reaching a place where a large section of roof is gone, Bacon stops under the open sky and shouts words that the investigators do not recognize. Alex and Aubrey take several shots at him, but with no apparent effect. As the do so, they twice see his outline blur and darken in a way that cannot entirely be explained by shadows and moonlight. He is drawing something from the inside pocket of his coat when Tuck slams into him. As he goes down, something flies from his hand and lands on the ground nearby.

Bacon manages to get to his feet, and there are a few seconds of confused melee as he tries to get away. It ends with a flying tackle by Tuck that brings his head down hard on a lump of concrete. Bacon is left unconscious and bleeding slightly. Ludwig examines him and finds that his condition is serious. He needs to be examined in a hospital as soon as possible; it would be dangerous to try to move him without a stretcher and an ambulance. While Georgina is dispatched to find a police box and report gun shots from the warehouse, Aubrey goes through Bacon's pockets. He finds only a bunch of keys; no money or identification. The object that flew from his hand turns out to be another whistle, which the investigators are understandably reluctant to handle.

Leaving the scene before the police arrive, they return to Bacon's house and let themselves in with their new-found keys. Inside, the house is shabby but almost obsessively clean and tidy, and it gradually becomes clear that every major object - books, furniture, and even the cutlery in the kitchen - carries a neat handwritten label with several coloured dots and a number.

The ground floor is mostly filled with stacked furniture, which Alex declares antique but not of particularly high quality. In the kitchen they notice a strong smell of fresh earth with a metallic undertone, which they trace to the coal cellar. Disappointingly, this proves to be full of coal and nothing else. The first floor is given over entirely to books of all kinds, with a heavy emphasis on anthropology, folklore, and the occult. The books are neatly arranged and labeled, but are not shelved in any obvious order.

The top floor consists of two rooms, both kept locked. The smaller is a bedroom, although the bed itself is only a frame and mattress. The neatly-labeled wardrobe and drawers contain clothes in labeled paper packets or labeled hangers. On the bedside table is a curious metal object about a foot long. It resembles a tuning-fork with one arm shorter than the other, engraved all over with curious glyphs or characters. The other room is a large study, with a writing-desk and many shelves of notebooks. On entering, Aubrey experiences a disturbing vision, but this is not shared by the others.

The investigators spend several hours searching the house, giving particular attention to the study. The most significant find is "The Turner Codex", left open on a reading stand. This purports to be a translation of a ninth-century Mayan text found in Guatemala. In a brief skim of the book, Aubrey finds prayers to an entity called Kaiwan or Hastur, and instructions for making something called the "Chime of Tezchaptl", whose description matches the object found in the bedroom. One bookcase in the study holds a catalogue in many volumes of all the labels in the house, but on careful study it proves useless. The labels are recorded and extensively cross-referenced, but only in relation to other labels; there is no actual list of objects. Georgina's search of the notebooks is more profitable, turning up several shelves of handwritten notes that appear to relate to the Turner Codex.

By this time, the smell of earth has become strong enough to reach the top floor, and the investigators are occasionally troubled by things moving at the edge of their vision. It is not possible to see clearly but there is an impression of one or more greyish things, rather larger and more bulky than a cat, that scuttle with curious rapidity along the floor or (on at least one occasion) the ceiling. They decide to gather up what they can carry and leave; this includes the Chime, the Turner Codex, and several bags of notebooks.

The next day, Ludwig makes discreet inquiries around the London hospitals about head injury cases admitted overnight. An unidentified man whose description matched Bacon was admitted to the North London Hospital, but never regained consciousness. The investigators decide to return to Bacon's house and continue their search while the police remain unaware, but are disappointed. The house has been ransacked, and the greater part of Bacon's library and notebooks are missing. This is not the result of a professional search - many items and much of the furniture have been broken, apparently without rhyme or reason.