The Blackthorn Key

Christopher and Tom study the message: "JSYYAALYUFMIYZFT" (137), which Christopher knows can't be in Latin because Latin does not use the letter J. They wonder about the meaning of the symbols at the beginning, which are a sword and a triangle, but Christopher does not understand it. He feels that he has let Master Benedict down.

Christopher helps Tom scrub the stairs, wondering what the code means. He has not sought out Hugh because of the message not to tell anyone, but Christopher realizes that Master Benedict used a code that Hugh would have known. While he is torn about whether to find Hugh, he knows he needs help to decipher the code. Christopher and Tom go to find Hugh, whose offices are with the doctor he works for, Nicholas Lange. However, Hugh is not home. They do see Dr. Lange and his wife, but he has not seen Hugh since Tuesday. 

Alone again, Christopher tells Tom that Hugh is not the murderer. He thinks Hugh may have gone to the country to visit his family. Christopher wonders if Master Benedict's first attack sent Hugh to the country. They go back to Tom's house, where his mother greets them with a sack of baked goods. Tom indicates that these go to a bedraggled man Christopher recognizes as Dr. Parrett, whose house burned down the previous year but who still lives there. Dr. Parrett approaches them, discussing his son who died in the fire as though he were still alive. Tom gives him the baked goods and tells him not to worry when he cannot pay immediately. 

Tom calls for his sisters and the family sits down to dinner with Christopher, though Tom's father still begrudges the fact that Christopher is there. Afterward, the boys clean up so that Christopher can earn his keep. The girls usually do this, and Cecily, Tom's oldest sister, enjoys correcting them. Later, Christopher reads the children a story about King Arthur before they go to bed. When they are done, Tom asks Christopher what his plan is because he recognizes the scheming look in his eyes. Christopher is planning to get his puzzle cube back.

Christopher and Tom sneak through the streets, even though it is dangerous at night. When they arrive at the apothecary's shop, Christopher uses a key that Master Benedict hid in a brick marked with the symbol for Mars because the Guild has taken his shop key. Bridget the pigeon comes down to meet them, and Christopher realizes that the coop on the roof is open and that the other birds are gone.

Trying the back door, Christopher notices it is unlocked. Inside, someone has been through the shop, and it is a mess. Tom urges Christopher to leave, but Christopher goes in, though he is crying. He finds Master Benedict's sash and ties it on, then finds his puzzle cube. When Bridget starts to eat some loose crystals, he is alarmed but soon realizes that they are only sugar. This leads him to realize that only the dry ingredients have been scattered in the shop and that the thieves must have been searching for something hidden because they have left all of the valuable ingredients there. Furthermore, this means they are literate because they can read the jars' labels. The boys start to leave when they hear something strange.

A voice calls out from the other room, wondering if his master is there. Hiding under the table, Christopher recognizes the red-headed apprentice he saw in the shop the other day. Nathaniel Stubb comes in, calling for Wat, the apprentice. Stubb is distressed at the sight of the shop and the cost of the contents. Wat responds he was looking for the fire as instructed but didn’t find anything. Stubb insists that it must be there, and that Master Benedict would have given its location away if Wat hadn't killed him so fast. 

Wat's response indicates that Master Benedict chewed madapple, killing himself before he could reveal any information. Christopher does not understand why Master Benedict would do that. Stubb rebukes Wat for not questioning Christopher when he had the chance, but Wat thinks Christopher did not know anything. Christopher realizes this is why Master Benedict hit him: to prove that they were not close and that Christopher knew none of his secrets. Stubb instructs Wat to find and question Christopher. 

When the men begin examining the shop's contents, Christopher thinks that he and Tom can escape before realizing that he left the shop key on the counter. Stubb is blocking the door, but if Christopher can move him, they can get out. Christopher gives Bridget to Tom, then crawls near the fireplace. Using ingredients in the sash, he quickly makes gunpowder and lights it in the fireplace. In the commotion from the explosion, Christopher and Tom escape. The boys run back to Tom's house with Bridget. No alarm has been raised, so Christopher knows the fire was contained to the shop. Tom wonders if they are safe, but Christopher is unsure.