The Blackthorn Key

Mercury has a double meaning in The Blackthorn Key: It is simultaneously a planet and a substance otherwise known as quicksilver. Sands plays on this double meaning by having Master Benedict use Mercury as a symbol twice: once in the puzzle cube and once in the mural opening the crypt to his secret workshop. By using the symbol twice, Master Benedict ensures that Christopher understands its significance so that he can use it when it really counts—in finding the recipe for the Prima Materia. This also allows the reader to solve the mystery along with Christopher, as his early experiences with the symbol prove relevant to the larger mystery.

Like other symbols in the novel, the puzzle cube that Master Benedict gives to Christopher has multiple meanings. It is simultaneously a gift, representing his esteem and appreciation of Christopher, and a challenge, meant to teach Christopher how to solve certain ciphers. With this personal gift, Master Benedict also gets Christopher to start thinking about the multiple meanings of Mercury. This tip will help him solve his master’s murder by ensuring that he understands how to open the vault beneath the mausoleum.

The sash that Master Benedict wears around his waist contains numerous substances that an apothecary uses on a daily basis. When Master Benedict dies, Christopher begins wearing the sash. This represents how Master Benedict’s position as apothecary and its attendant responsibilities have become Christopher’s. As Christopher explores the materials in the sash, using some to save himself from being trapped in the Guild Hall, he begins to master them. This shows that he is accepting the knowledge and responsibilities left to him. 

Before Master Benedict dies, he writes a final message to Christopher on the last page of the ledger. To do this, he uses several codes that only Christopher can decipher. By doing so, he illustrates his confidence that Christopher has absorbed the lessons Master Benedict has given him. More importantly, he shows that he trusts Christopher with the apothecary’s secret: the recipe for the Prima Materia. Christopher immediately understands that the message is meant only for him, keeping it from the eyes of the Guild members and even Lord Ashcombe. This further emphasizes the loyalty and responsibility he offers to Master Benedict in exchange for what Master Benedict has offered him.

Madapple is one of the first substances that Christopher learns about as an apprentice. Master Benedict uses it to show him that substances have different properties in different quantities, and that the apothecary’s responsibility is great. Master Benedict underscores this lesson by killing himself with madapple rather than letting himself be tortured and perhaps revealing the secrets of the Archangel’s Fire. By doing so, he reminds Christopher that their knowledge comes with responsibility to others and should not be taken lightly.