how does mr halloway figure out who jed is?

Mr. Dark's final incarnation in the novel is as a boy named Jed. As Jed, Mr. Dark attempts to lure Mr. Halloway away from Will and Jim, but is ultimately foiled by Mr. Halloway's refusal to allow Evil any power. In the face of such disbelief, Mr. Dark dies. This is an important element of his character and an important lesson in the context of the novel as a whole. His death suggests that his evil existence depends on people's fear of Evil. That is, as soon as we refuse to give fear any power, fear goes away. Sounds like a good deal to us.

•The boy says it is Jed and hurries Charles Halloway forward, saying there's very little time left. Charles asks for Jed's age. Jed says he is nine.

•Charles calls Jed out on the deadfall. He says that sometimes good has all the weapons, and sometimes people can't be picked off the way Jed is trying to now.

•Jed leaps away but Charles is too quick. He has gotten hold of Jed's shirt. Jed's small body is covered with tattoos. It is Mr. Dark is disguise.

•Charles clamps down on Jed and gives him a talking-to. Jed cries. He cannot stand being near Charles Halloway. Charles volunteers to spare Jed if he can tell them what is wrong with Jim.

•Jed squirms and says he cannot.

•Charles gathers the boy closer and thinks to himself that evil has only the power we give it.

•Eventually the light in the boy's eyes dim and the body rustles to the ground.