The Blackthorn Key

At the bottom of an extremely long staircase, Christopher, Tom and Isaac reach a room with enormous carved doors. Isaac asks Tom to open them, surprising Tom by using his name. He explains that Master Benedict described Tom to him. Inside the door, they find a huge room with many shelves of books, scrolls, and stone tablets everywhere. Isaac tells them that they are in a space the Knights Templar built beneath the city to store their treasures. Since then, the gold has disappeared, but they have replaced it with new treasures: the books. Christopher asks who "we" are, and Isaac clarifies that there were seven in his group of alchemists, including Master Benedict.

Christopher says that he thought alchemists were charlatans who claimed to turn lead into gold. Isaac clarifies that they looked for the answers to many secrets. He then takes the boys to a book, explaining that the alchemists are seeking the Prima Materia, the First Matter, "the raw energy from which Our Lord created the universe" (288). Because life is built from this Matter, an alchemist who could access it would be able to direct its powers. The book he pulls out has an ouroboros on the cover, a symbol of the Prima Materia. Christopher realizes that Master Benedict was looking for it, and Isaac clarifies that Christopher is too, even if he doesn't know it yet, because Master Benedict wanted him too. Christopher starts to reveal information about the crypt, but Isaac stops him, saying that the alchemists maintain some secrets amongst themselves. Christopher worries the Cult will come after Isaac, but Isaac trusts his fate.

Christopher again asks about the key, and Isaac explains that the symbols are alchemical except for the symbol of the sword, which represents Archangel Michael. Tom wonders if alchemists are in the Cult, but Isaac states that the Cult does not exist and that the murders were just committed by bad men. This is one reason the alchemists work in secret, because people like the killers can appropriate their mission for evil purposes.

Isaac directs Christopher to another book. Inside, Christopher finds a chart in Master Benedict's handwriting. Isaac warns Christopher that the work he is doing is dangerous and that his choice may lead to suffering. The killers want power. He describes Archangel Michael, who led heaven's armies against hell's. God gave him the First Matter, also known as the Archangel's Fire, for this purpose: "the raw essence of the Prima Materia. It is God's power unchecked" (293). Isaac explains that this is what the killers want but should never get. He tells the boys about knights, who stopped fighting after the invention of guns made them powerless. He goes on to explain that using the Archangel's Fire would have a similar effect on warfare: "An army that walks with the Archangel will be invincible" (294).

Christopher and Tom go back to the crypt under the mausoleum. Now that they have seen the materials at Isaac's shop, they understand the symbols of the ouroboros, the Archangel, and the dragons. They have an extensive chart, the "Vocabularium Alchemiae," which decodes various symbols: The Three Principles, The Four Elements, Planetary Metals, Terrestrial Minerals, Corrosives, Weights & Minerals, and Instructions/Processes. Together, they decode the message. 

Because they already have the first clue, mercury, they look at the second: air. This initially confuses them because the hole is already empty—filled with air. Christopher realizes that this means that nothing should go in there. For the last symbol, Christopher decodes that they need to mix water and salt. Once they do this, the boys pour the chemicals into the door and it opens.

The door leads them to a passage and another door. First, they turn to look at the mechanism of the first door, which works through a series of levers and counterweights. The saltwater went into a jar, producing sparks. Behind the next door, they find an apothecary's workspace with an oven, an ice vault, and other preparation areas. There are three additional doors, as well as several planks with notes on them. Christopher identifies these as failed recipes: some in Master Benedict's writing, some in Hugh's, and some in others. In addition, they find many papers, going back a long time. 

As Christopher goes through the notes, Tom finds a lot of dried blood in front of one of the open doors. Inside, the walls have been burned, and there is a beaker with a yellow liquid that Christopher can't identify. It feels oily and tastes sweet. Lengths of cannon fuse surround it. Most importantly, they find a cylinder surrounded by greased parchment with a fuse in it and a bucket full of sawdust nearby. The sawdust reminds Christopher of cleaning up on Oak Apple Day.  

Christopher looks through Master Benedict's notes on the table, which are all about how to create the Archangel's Fire. He tells Tom what he's discovered, starting to feel ill. Back in the main workroom, Christopher starts to read his master's notes and sees that Master Benedict identified sawdust as the key to keeping the material stable. Going to the top of the notes, he sees that Master Benedict believed the power of the Archangel's Fire was too much for any person to control. Christopher realizes that the burned room used to be a testing room for the Archangel's Fire. He calls for Tom, who is still in the room, and Tom jostles the table, upsetting the beaker. Christopher pulls him out of the room as the beaker falls to the floor and explodes.

Christopher wakes up on the floor, trying to remember how he got there, his head ringing. For a second, he doesn't recognize Tom. The door has blown off its hinges, and a fire is going. Christopher pours sand over it and checks on Tom. His senses coming back to him, Christopher realizes the blood on the floor is Hugh's. Hugh wasn't murdered but rather died in the process of testing the Archangel's Fire. He feels bad for Master Benedict, who couldn't tell anyone about the loss of his former apothecary and who kept searching for the right formula to tame the Fire. Finally, Master Benedict found it by using sawdust. 

Christopher feels proud that his master trusted him and that he made the choice to stay. At the same time, he feels the weight of responsibility that his master placed the future of the Archangel's Fire with him. Christopher considers the danger of the Fire and his responsibilities. The Fire would create an unstoppable military force. Thinking about Watt, Martin, the Elephant, and Stubb, Christopher understands the murders and the Cult and makes a plan.

Later, Christopher finishes writing two letters as Tom warns him about the danger. He sends Tom off with the letters anyway, telling him not to come back. Tom protests but eventually promises to stay away. He will deliver the first letter at nine o’clock in the morning and the second at eleven o’clock in the morning. Before leaving, he hugs Christopher. Alone, Christopher follows the recipe, using a supply of the sweet syrup his master made. When he is finished, he goes outside and waits.