Published in 2015, The Blackthorn Key is a children’s historical fantasy novel by Kevin Sands. Set in 17th-century London, the story follows Christopher Rowe, the young apprentice to a successful apothecary, as he puts all his skills to the test to uncover a terrible secret that is threatening the city’s apothecaries. After earning his degree in theoretical physics, Sands has worked as a business consultant and teacher. The Blackthorn Key, his debut novel, is the first book in his award-winning series of the same name.

Plot Summary

Fourteen-year-old orphan Christopher, the first-person narrator, recognizes his good fortune at being chosen as apprentice to Master Benedict Blackthorn, a talented apothecary. While Christopher’s experiments sometimes get him into trouble, Master Benedict treats him strictly but fairly. Furthermore, Master Benedict educates him about everything an apothecary needs to know, from ciphers to Latin. 

When Christopher goes too far and deciphers his master’s code for gunpowder, Christopher and his friend Tom Bailey create a mess in the shop. Christopher cleans it up, in the process overhearing a conversation between Master Benedict and Nathaniel Stubb, a competing apothecary. From this conversation, Christopher learns that six men, primarily apothecaries, have been murdered by a group publicly known as the Cult of the Archangel. While this scares Christopher, it does not immediately affect him. However, later that day, Master Benedict and his former apprentice Hugh go out; when Master Benedict returns, he is injured. As Christopher treats his wounds, Master Benedict asks if Christopher is happy or would rather have a different life—but Christopher is content.

The tension rises when, the following day, the normally kind Master Benedict suddenly becomes enraged at Christopher in front of a group of customers. Striking him, Master Benedict sends Christopher on an errand for an ingredient he claims Christopher has forgotten, but which Christopher is sure he did not. By the time Christopher returns to the shop, Master Benedict has been murdered. There are no immediate clues—except for a coded message Master Benedict has left for Christopher on a ledger page.

Christopher begins the search for his mentor's murderer. However, authorities (including Lord Richard Ashcombe, working on behalf of the king) believe that Christopher may have killed Master Benedict for mistreating him. Christopher must find the real murderer to avenge himself. To do this, he turns to the Apothecary Guild’s council, which includes Oswyn Colthurst. Oswyn was responsible for seeing Christopher’s potential and placing him as an apprentice. The Guild members try to reassure Christopher that, although there is no Cult, apothecaries are trying to find the Fire of the Archangel, an incredibly strong substance that would give them inhuman powers. 

As the action rises, Christopher begins to decode Master Benedict’s message. He and Tom start to search for Hugh. Though Hugh is missing, the message leads the boys to a workspace hidden beneath a mausoleum. A charred room and a vial of liquid show Christopher that Master Benedict had found the Fire, causing his earlier injuries. However, when Christopher tries to find Oswyn to tell him about this, three apprentices try to murder Christopher. This plot twist, in which those supposedly on Christopher's side turn against him, reveals the truth to him. Christopher, always impetuous, shows character growth as he makes a well-thought-out plan. He lures Oswyn to the mausoleum, calling Lord Ashcombe there, as well. While Oswyn confesses, he has brought backup, and his men seriously injure Lord Ashcombe. Under seeming protest, Christopher shows Oswyn the crypt and the Fire.

In yet another twist, Christopher tricks his supposed captors. As Oswyn’s apprentice starts to light the Fire, setting off Christopher's trap, Christopher pulls Lord Ashcombe into an unlit oven beside him. In the book’s climax, the workshop explodes, destroying all antagonists. In the book’s falling action, Christopher and Lord Ashcombe recover from their injuries; Christopher is named heir to Master Benedict’s shop and will receive more training from another master, to be appointed later.

Through Christopher’s relationship with Master Benedict and his subsequent adventure, Sands touches upon themes of responsibility and loyalty, as well as the strength of the master/apprentice relationship. Christopher’s trajectory, which relies heavily upon decoding symbols and deception, shows both the value and the trickiness of such tactics. As he encounters representatives of institutions from the Guild to the Crown, Christopher also learns about the dualities of these institutions, which can be beneficial but also dangerous. Finally, Christopher’s success drives home Sands’ point that everyone and everything has value, no matter how overlooked it may normally be.