The Spook is talking to a lad's dad. We'll learn more about the Spook and the lad, like his name, later on. Just stick with us.
It seems that the lad is almost thirteen, and he's scared about becoming the Spook's apprentice. But since The Spook's Apprentice is the title of the book in the U.K, we don't think he'll back out.
The Spook agrees to take the lad on for a month trial. If he doesn't pass the trial, the Spook will return him and take "another guinea for [his] trouble" (1.24). That's right: The Spook charges a restocking fee.
That night, the lad, whose name is Tom, talks to his oldest brother, Jack, and his wife, Ellie. They tease him about being afraid of the dark and about how he'll never have friends if he's a Spook. But Ellie assures him that he'll always have his family.
After dinner, Tom has a talk with his Mam, who tells him that he has a gift and it's going to be his job to protect the County. Looks like his fate has been set in motion.