The mostly submerged Holland was headed toward the Upper Bay at six knots. Darbee fiddled with his motor. The noise deepened to an insistent growl, and the oyster scow doubled her speed. It halved the distance to the splashing handrails, halved it again, and pulled past the backwash of the submarine’s enormous propeller. Bell braced to jump to the conning tower. The wooden boat surged alongside. He could sense more than actually see the steel hull beneath the surface. He braced to jump, targeting the periscope tube, gambling that the thin tube was strong enough to hold him until he got a grip on the rails.

The Holland submarine disappeared.

One moment, the turret was just ahead of him. The next, it was gone, deep in the water. Bell could see trailing bubbles and the ripples from the propeller, but there was nothing to jump onto anymore, no turret, no rails, no periscope.

“Slow down,” Bell called to Darbee. “Follow his wake.”

Darbee throttled back to match the submarine’s six-knot speed.

Bell stood on the foredeck, watching the rhythmic swirls of propeller wash and signaling the old man when to nudge his tiller to the left or right. How the underwater ship was navigating its course was a mystery that was solved after they had gone half a mile. Shortly before the submarine reached the next bend in the channel, its periscope suddenly emerged from the water, and the submarine changed course.

The spy had plotted their route out of the Kill Van Kull by noting the time that would elapse between each turn. Bell signaled a similar change and the oyster scow turned with it. The periscope stayed above water. It swiveled around until its glass eye was facing him.

“Stop engine!” Bell shouted.

The oyster boat’s speed dropped as it drifted on momentum. Bell watched for signs that the Holland would back up or even turn around to ram them. But it held its course and pulled ahead of the scow, still showing its periscope.

“Darbee, did the test Holland you watched have a torpedo tube in back?”

“No,” Darbee answered to Bell’s relief, until he added, “I heard talk they might add one.”

“I can’t imagine he’d waste an entire torpedo on us.”

“Suppose not.”

“Speed up. Get closer.”

Ahead, the Kill took a sharp turn. The periscope swiveled around, and the unseen helmsman steered through it. Bell signaled for the oyster boat to accelerate. He drew within twenty yards of the stubby tube and the swirling propeller wash. But the water ahead was turning choppy as the Kill spread into the Upper Bay.