The secret: It’s connected to The Books of Conjury. 

It’s not, technically, a sequel—but an important thread from the trilogy runs into Ghost at Dusk. 

Readers of the trilogy will recall that after Finch and Swaine find Salem somewhat too dangerous to remain in, they move to the town of Andover, some 15 miles away. Now, that doesn’t quite solve all their problems with demons—what with the sorcery and Finch’s witch nature, a few demons continue to plague them. Various wards and glamours keep them at bay. 

Hume’s Eleventh Ward, used by Swaine during this period, possessed a peculiar side effect: While it can drive a demon away, sometimes it appeared to bind the demon to the area. Not always. Just sometimes. 

I set Ghost at Dusk in: Andover.

Where Tim Lane faces: a demon.

Tim sometimes wonders where Mister Groan (aka Scary Eyes, Flibber, and Mrs. Gracie) comes from. He doesn’t know.

But I think we know now, don’t we?

Oh, we do.

Astute readers may raise a clever objection: Swaine assures Finch that ghosts don’t exist. He’s emphatic on the point.

So is he wrong?

I’ll just say this—Finch knows as well as anyone that Swaine, a genius to be sure, had his blind spots.

Happy reading!