Earl Cain Hargreaves, a young nobleman with a passion for collecting poisons, lives in 19th Century London and fights against the machinations of his own father, who has founded an organization called Delilah, though for what end he does not know. Along the way, Cain discovered he had a half-brother named Jizabel Disraeli, who works for Delilah and carries out horrible experiments, although, again, to what end Cain doesn't know.
Cain's main allies include his manservant Riffael, also called "Riff", who guards Cain with his own life, and his ten-year old half-sister, Mary Weather, who despite living on the streets, has managed to retain most of her youthful innocence.
A new Pleasure Garden is opening in London, call the Crimone Garden, and to the shock and joy of most of the city, will be open even to the lowest members of society. The Garden is owned by the Barbara Company, which seems to be headed by Lord Gladstone, a philanthropist. But the Crimone Garden is the center of a series of sites owned by Delilah, which seem to be a reconstruction of the pattern of Stonehenge. Cain decides to investigate.
On the way to the carriage, Cain is nearly pickpocketed, but catches the thief. Mary knows the boy, whose name is Leroy. He helped her when she was living on the streets, destitute, with her mother. In thanks, Cain gives Leroy all the money in his wallet, which Leroy needs to help buy food for his sister. Leroy tries to scorn the money as Charity, but Cain and Mary convince him to accept it.
When Leroy returns to the sewers where he and his sister have been sleeping with the food, he finds his sister slain, and he is attacked by a mysterious figure. Meanwhile, Cain tracks down Lord Gladstone at the Opera, where he is attending with his silent ward, a girl who was burned and lost her voice in a fire. Gladstone has taken the girl in and is raising her to be better than her lower-class origins. Gladstone is glad to meet Cain, but his ward, Lady Latisha, seems to be a very angry young woman. She slaps Cain and throws her drink in his face when he is charming towards her.
Gladstone hypnotizes Cain and attempts to make Cain tell him why he is there at the Opera, but another thrown glass cuts off the attempt, and Gladstone invites Cain to his home to make up for Latisha's behavior. Cain agrees, even though he suspects it might be a trap.
Gladstone, also known as Head Priest Cassandra in the organization of Delilah, reveals that he has a plan in mind for the opening of the garden, and Cassian, another operative, is desperate to get a new body, because his old one is stuck in the size and shape of a child. Dr. Zenopia, another member of the organization, suggests his brain be transplanted into a fully adult body, but Gladstone pooh-poohs the idea and taunts Cassian about his size. Even though he looks like he is 10 or 12, Cassian is actually 36.
Cain arrives, with a poison in his watch, but he and Riff are separated right away. And when Mary Weather convinces her cousin Oscar, who Cain has set out to look after her, that it wouldn't hurt for her to go to the opening night at the Pleasure Garden, all their lives are in danger when Gladstone reveals his plan to cleanse London... by killing the poor, crippled and those he considers his "inferiors" by setting off fires and explosions in the park! Can Cain foil Gladstone's plans and save everyone in the park, including his sister?
This is unusual but enjoyable series. Cain can be cold and seem emotionless, but there is no doubt that he truly loves his half-sister, and that Riff, his manservant, is as close to him as a lover (We can't really say "father" as his father hates Cain and wants to kill him).
Despite Cain's failings as a warm character, it is intriguing to see the various plots of Delilah unfold, and how Cain manages to foil their ultimate outcome, as well as bringing the author of the plot to ultimate justice. Often, this justice isn't at his own hands, but those of the planner's fellow conspirators or their superiors.
The book ends with a short story not tied to Delilah or its machinations, about a woman seeking refuge from a man who once loved her and promised to marry her, giving her his family's ring. But he had lost his memory, and when he got it back, he realized he was promised in marriage to another woman from a family as rich as his own. He'll do anything to get his ring back, even kill her.
Will he rethink his position when Cain comes to give him what he wants?
Like many of the stories involving Cain, this one has a sad, but poetic ending, and is based around the old rhyme "Solomon Grundy". Cain, at the end, appears unmoved by it all.