"Where did Peter want me to go next?" she asked, losing interest, replacing the cap on her lens.

I tried to recall exactly what Quinnell's instructions had been, at breakfast. "Well, I think he said they were going to start a new trench where the principia ought to be, and he wanted you to take a photograph before they stripped away the sod and topsoil."

Fabia frowned. "But we're in the Principia."

“No, he means the real one.'' When she still looked blank, I stared in open disbelief. "Don't tell me you're Peter Quinnell's granddaughter and you've never learned the layout of a basic Roman fortress?"

"Well, I—"

"Oh, Fabia!"

"It's like I said. My father hated all this stuff, and Peter just assumes I ought to know."

"Then for heaven's sake, come here," I said, "and let me sketch it out for you." Pencil in hand, I tugged an unimportant letter from one of the stacks on my desk and turned it over to its blank side. "Here, the average fortress looks like this—you see? A bit rectangular, with rounded corners, like a playing card. A ditch, sometimes a double ditch, outside, and then the ramparts, with a guard tower at each corner. Now ..." I took my pencil and drew a square, bang in the center. "The principia, or headquarters building, is here. And running right along in front of it is the via principatis, that's the road that links the fortress's two side gates." I sketched in the gates, too, to keep things absolutely clear. "From the front gate to the headquarters is another road, the via praetoria. And from the headquarters to the back gate, there's the via decumana. Now, here," I said, drawing in another square to the left of the principia, "you'd have the granaries, and maybe a workshop. And on the other side of the headquarters building would be the praetorium."

"What's that?" Fabia asked, showing a faint spark of interest that made me think she might not yet be past all hope.

"The commander's house. And then the hospital is usually sort of in this spot right here, and most of the rest would be barrack blocks, and stables for horses." I filled in the hollow spaces above and below the principia with neat rectangles, to show her.

She leaned over to study my drawing. "So it's really just barracks, and then this row of important buildings, and then more barracks, with a few criss-crossed streets."

"Pretty much," I agreed, smiling at her dismissal of the brilliant efficiency of Roman military planning.

"And this is where we started digging, isn't it? Down here, at this guard tower?"

"Indeed it is."

"So ..." Her finger trailed up the makeshift map, toward the center. "Peter's going to start his new trench up in here, somewhere."

"It shouldn't be too hard to find," I assured her. "Just look for a big bunch of people with spades."

She took my drawing anyway, tucking it into one pocket of her shorts while she gathered up her camera and equipment. When she'd gone, I put my pencil down and stretched, trying to ease the knot between my shoulders. My two young assistants were outside, manning the water flotation tank that Peter had installed behind the building. An upright, barrel-shaped device with hoses attached for fresh water and drainage, it sifted excavated soil through screens so fine that we could then recover tiny seeds and insect parts, as well as bits of pottery or bone. Bone, I thought, would have been useful. A nice full skeleton, clad in legionary armor, with an ancient Scottish sword still buried in its skull...

But Robbie had said that there weren't any bones in our field. That struck me as odd. If the Sentinel was, as he claimed to be, a soldier of the Ninth, and if the Ninth had truly perished here, then there ought to be bones, and plenty of them.

A high-pitched snatch of laughter floated in through the long back wall, from where my two students were working. I sighed, and pushed back my chair. As finds supervisor, I reminded myself, I ought properly to be out there with them, supervising, instead of hiding in here like a coward.

The outdoors looked harmless enough, the field an anthill of activity beneath a sky of rolling cloud and brilliant bursts of blue. David was down by the road, by the thorn hedge, crouched over a bit of newly exposed earth that a few of the students were clearing with brushes. More post holes, I speculated. They'd found the edge of what appeared to be one of the barrack blocks yesterday.

Peter, hoping to find some evidence of the Ninth's presence in the fortress's principia, stood now like stout Cortez upon a subtle rise of ground near the center of our carefully staked site, directing Fabia's photography.

Surely any ghost would find activity like that far more interesting than my own boring little scribbles in the finds register. Bolstered by that thought, I turned my back to the field and took a tentative step away from the stable door.

I stopped. Paused. Listened.

Nothing followed but the breeze, and even that was brightly cheerful, not the least bit cold or threatening. The laughter drifted out again from the far side of the building, and I set my shoulders, walking on more bravely now along the long front wall of our Principia. Just around that corner, I promised myself, hating my sudden nervousness. Just around that corner, and up the deeply shaded side wall, and around another corner, and I'd be with people again.

Still, before I left the sunlight and the full sight of the field, I stopped again and listened for the fall of ghostly footsteps. And only when I was satisfied that there was no sound but the distant voices of the dig and the trilling warble of a songbird in the trees ahead of me ... only then did I turn the first corner.