This concludes (what exists of)
The Secret of the Cave

What happens next?
Well, I don't know yet. I'd much rather let myself get pulled into the direction that excites me each day, let the river take me where the river flows, than have a fixed plan that I have to stick by, rigid, like a highway.

If I had to tell you right now, I'd say Aquila exits (we never see where she came from or where she goes), Inger Lint takes her word for it that Avi is good people, and lets Avi in on the titular secret of the cave -- a large-scale network of tunnels and doors, some of which we see inside, beneath the forest, possibly stretching as far as the city.

When Avi returns the next day, the hatch, naturally, is gone.

And after that?
Well, read on...

From the start...