Here is the summary of the book:
As danger increases in the County, Tom is sent far north by his master to be trained by Bill Arkwright, another Spook. Arkwright lives in a haunted mill on the edge of a treacherous marsh and his training methods prove to be harsh and sometimes cruel. But he has toughened up many previous apprentices and now he must do the same for Tom and prepare him for the gravest dangers of his life. But when the Fiend sends his own daughter, the ancient powerful water witch Morwena, to destroy Tom, Arkwright makes an error of judgement and Tom finds himself facing his enemies alone. The Spook and Alice realising his danger, hasten to his aid but will even their combined strengths suffice in the face of such terrible dark power? And what is the Spook's mistake, the consequences of which might give final victory to the dark?
The dark made flesh is loose in the world and things are going rather bad in the war, the County soldiers wage against the invaders and so the army needs young men and as seen in a lot of historical accounts of the soldiers forcing young children into battle, so we see the same here. Thus, to prevent Tom from being pressured to join the army, the Spook sends him north to train with Bill Arckwright for 6 months.
A short into to Bill Arckwright. He is gruff, very hard, knows how to deal with the things that come out of the water, one of the few who were able to complete their apprenticeship with the Spook and has got got a serious drinking fetish. Arckwright is none too keen to take on Tom for a six months tenure but he does out of gratitude to the Spook. Tom's first impression of his new master is none too kind, Arckwright is the polar opposite of the Spook in their way of handling things but Tom does as he is asked. After a series of mishandling and rising curiosity on Tom's part, he finally finds out why his new master acts as he does and they both vow to lay off their differences and work together.
Reasons? The threat of the fiend still looms large and even if it is said that the fiend won't come after him again since the witches could only control old Nick for 2 days but when he sends his daughter Morwena or better known as the bloodeye, can Arckwright's decision hold true or does he need to change his ways before its too late.
The Spook's Mistake follows shortly after the previous and don't think I told you all everything that is in the book in the above paragraph because it is not. For while Tom learns to adapt to a new master, more secrets that you may not have previously thought to exist are revealed and new allegiances are forged in a bid to battle the fiend's daughter and the true nature of the Spook's mistake is revealed, it may well be long lasting.
"Can Tom survive the harsh North and his new master...."