Mark of the Plague: Blackthorn Key, Book 2

Book review by
Mary Eisenhart, Common Sense Media
Mark of the Plague: Blackthorn Key, Book 2 Book Poster Image
Teens fight plague, pursue murderers in thrilling sequel.

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age 10+
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The parents' guide to what's in this book.

Educational Value

Besides offering a lot of period detail of daily life in 1600s London, Mark of the Plague teaches valuable lessons about critical thinking and sifting through evidence, rather than fear and speculation, being the best tools to solve big problems. There's a smattering of Latin and a bit of chemistry (including the recipe for gunpowder), as well as a discussion of codes and encryption, with examples. Puzzle-loving readers will love figuring out hidden messages -- maybe before Christopher does.

Positive Messages

As in Book 1, friendship, loyalty, and doing the right thing in spite of pressure to do the wrong one are important themes. Author Kevin Sands, a physicist by training, delivers strong but not heavy-handed messages about using your brain to solve problems -- and also to look critically at "magic" occurrences to determine the science and/or trickery involved. There's a lot of practical wisdom as Christopher recalls his late master's lessons: When it's impossible to figure something out, "I step out of the way, and let my mind find the answer for me."

Positive Role Models & Representations

There's a lot to love about the lead characters here, including the faithful and clever pigeon Bridget. Protagonist-narrator Christopher is very relatable as he struggles with ethical dilemmas (for example, more than once he turns away large sums of money because it would mean doing something he considered wrong) and tries to be kind and helpful to friends and strangers alike as the plague rages. Normally law-abiding, he breaks the law that demands he kill Bridget. Friends Tom and Sally are brave and loyal, and the teens work well as a team. The late, lamented Master Blackthorn, seen in dreams and memories, is a loving, supportive teacher.


The Black Death is killing people by the thousands, and there's vivid description of its gruesome symptoms and torments, as well as dead bodies. Also, it soon becomes clear that some of the "plague" deaths are actually murder, and there's a race to bring the killers to justice before they strike again. Due to the plague, Londoners have been ordered to kill all their animals, so Christopher's constantly challenged to keep Bridget safe. Over the course of the story, the kids suffer beatings, stabbings, poisonings, and broken bones; adult characters perish in an exploding house, and another is lynched by a mob. Pistols and swords are brandished. The villains take the teens captive and threaten to torture them.


Readers may begin to suspect a future romance between Christopher and Sally, but it's only the faintest glimmer for the characters themselves, who tend to be distracted with other matters.


There's no plumbing in this era, so there are many references to pee, poop, and raw sewage in the streets. Pigeon poop is valued for producing saltpeter, an ingredient in gunpowder. In one scene, the kids take advantage of the fact that a guard is relieving himself to sneak into a building.


Some references to Book 1 as background to events in this story.

Drinking, Drugs & Smoking

In keeping with the era, people of all ages consume wine and ale. As an apothecary, Christopher makes and administers medications, including "poppy" (opium) to relieve a friend's serious pain, as well as antidotes to poison.

What parents need to know

Parents need to know that Mark of the Plague is physicist-turned-author Kevin Sands' follow-up to the much-honored The Blackthorn Key, with its teen protagonists facing new dangers and struggling to solve new mysteries in 1665 London. One mystery: Who is this stranger who seems to be able to cure the bubonic plague that's ravaging the city -- and what's in his medicine? Another: Where (and what) is the mysterious treasure left to 14-year-old Christopher by his late master? As the plot unfolds against a backdrop of the black plague's devastation, the teens suffer beatings, stabbings, poisonings, and more in their efforts to discover and unmask a murderer. Like in Book 1, Mark of the Plague delivers swashbuckling adventure, brain-teasing puzzles, several explosions, and assorted gun-brandishing and sword-wielding. As in Book 1, the narrator gives the recipe for gunpowder. Pee and poop abound, sometimes as part of the pre-plumbing scenery and sometimes as a chemical ingredient. Some characters die, and there are brief gory descriptions of injuries and plague symptoms as well as dead bodies. Also as in Book 1, this installment has a strong moral compass, with frequent but non-preachy messages about friendship, loyalty, kindness, using your brain, and doing the right thing even when you're being strongly pressured to do the wrong one.

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Kid, 9 years old April 15, 2017
Actually I give six stars, but that wasn't an option. Even better that book 1, much more was happening. Spoiler warning! I guessed that Henry was bad, but... Continue reading

What's the story?

THE MARK OF THE PLAGUE follows the events of Book 1, and 14-year-old Christopher Rowe should be enjoying a happy and prosperous life in the London apothecary shop left to him by his murdered master, Benedict Blackthorn. But 1665 London is now in the throes of an epidemic that kills thousands each day -- and brings a horde of charlatans and predators exploiting the people's fear with pricey fake cures and "magic" charms. Impoverished Christopher learns that his late master has left him a "treasure" -- and only the most mysterious hints about where to find it. With people suffering and dying all around them, Christopher and his best friend Tom, along with fellow orphanage alum Sally and the faithful pigeon Bridget, race to find the treasure and the truth -- which is hard, when almost nothing and no one are what they seem, and the plague can strike anyone. Swordplay, explosions, mob violence, and other deadly perils ensue as the friends try to identify the villains, foil them, and not die in the attempt.

Is it any good?

Kevin Sands delivers a thrilling sequel with appealing teen (and bird) heroes, creepy villains, challenging puzzles, and plenty of mortal danger. It's easy to root for apothecary-in-training Christopher and his friends as they try to solve mysterious puzzles, decipher coded messages, and stop murderous villains as The Mark of the Plague falls upon its luckless victims. Sands' vivid descriptions plunge the reader into the often-scary world of London in 1665 -- and offer a lot of humor when, say, a lab experiment doesn't exactly go as planned.

As in the first book, there's the occasional too-modern howler -- in this case, numerous references to "paranoia." But it doesn't break the spell as the young heroes pursue truth, justice, and a cure for a horrible disease.

Talk to your kids about ...

  • Many fictional stories take place in the time of the Black Death or other epidemics. Stories such as Mark of the Plague show how such times bring out the best and worst in people. Do you know any other examples?

  • Do you like codes and ciphers? How would you make up a code that was easy to understand for everybody in the know -- and completely impossible for everyone else?

  • Does reading about Christopher's adventures in the lab make you want to do chemistry experiments? What would you like to try first?

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For kids who love historical fiction and mysteries

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