“I really am taking this thing off.” Marino continues staring down at the heavy hunk of plastic as if it is a bomb or a giant leech.

“The pelvic bone, the clavicles, the sternum. Hard points of the body that can sustain several thousand pounds of force.” I sound as if I’m delivering an anatomy lecture, and I sense the crewmen listening. “How many seat belt injuries have you seen? Thousands,” I reply above thundering outboard engines as I check my e-mail again. “Especially when the lap belt ends up around the abdomen instead of low around the hips, and in a collision what happens? All that force is directed at soft tissue and internal organs. That’s why we wear harnesses like this.”

“What are we going to run into out here? A fucking whale?” Marino exclaims.

“I certainly hope not.”

We speed through a light chop, past long fingers of wharfs and piers that date back to Paul Revere as a British Air 777 roars low overhead, inbound for Logan to the east, its runways surrounded by water and barely above sea level. Off our starboard side Boston’s financial district sparkles against the bright blue sky, and behind us, rising above the Navy Yard in Charlestown, the Bunker Hill memorial looks like a stony version of the Washington Monument.

“Let’s just see,” I say to Marino. “We’re what? Maybe a quarter of a mile from the terminals?”

“Not even.” He sits tightly strapped in his chair, staring through water-splashed Plexiglas.

The airport is sprawled over thousands of acres that jut out into the water, the air traffic control tower’s windowed floors supported by two concrete columns that remind me of stilts. Two intersecting runways extend far out into the harbor, their stony embankments remarkably close, not even a hundred feet to our left, I estimate.

“Depends on where the LAN is located, of course,” I add, as I go into settings on my iPhone and turn on Wi-Fi. “But I know for sure I’ve been stuck in planes on the runway before and accessed Logan’s wireless. Nothing out here, though,” I observe over the noise of engines and the boat bottom thudding the water. “Logan’s signal has dropped off. So if the person sent the e-mail from a boat, for example, I’m going to suspect it was practically right up on the rocks, right up next to the runway.”

“Maybe someone sent it from a boat that has a router,” Marino suggests.

“Lucy is absolutely sure it was sent from an iPhone. But I suppose it could have been synced with a router, making it easier to access an unsecured network,” I consider, as we pass the curved glass building of the federal courthouse and its public park at Fan Pier.

I check my e-mail again. Nothing, and I write another note to Dan Steward, letting him know I’m en route to a death scene and will have to take care of what I suspect will be a complicated autopsy when I return to the office. Please confirm whether I need to show up at two p.m. as planned, and I continue to hope my presence won’t be required after all. I hope it rather desperately.