While Henry Makepiece shifted through the ashes of an extremely charred plane, Agent Parker was poring through the boxes from George McInroe’s house, and Officer Carlisle was gloomily surveying an array of brochures on mounted police training. But it seems like such a nice day, and really there’s no reason to be inside with them, because they won’t be going anywhere any time soon. Well, Henry and Agent Parker are in a different time zone than Officer Carlisle, so they’ll be going to lunch pretty soon, but that won’t be very exciting (Henry’s having a peanut butter and jelly on rye, Agent Parker is having tapas at a trendy little bar tucked away in a corner of Capitol Hill which hasn’t been found by any ravenous Congresspeople yet).

On this shimmering and beautiful morning, Mr. Delaney’s class of AP Biology students was suiting up in wetsuits on the pier, getting ready to hop into kayaks and start rowing upstream to take water samples. He had suggested the sampling as an interesting extra-credit project which could be passed down to future classes, creating an extensive record which could be useful at some point, expecting a few particularly obsequious students to pitch in, and was surprised when the whole class pitched in.

Cassandra White, known to her classmates as Cassie, had even suggested doing fish counts as well, arguing that the water samples would be more interesting in context, and before Mr. Delaney knew what was happening, he’d gotten a grant from Fish and Wildlife and the donated use of a fleet of electric orange kayaks. This being that sort of town, most of the students had wetsuits already, and the few who didn’t borrowed them from classmates, or the dive shop, in the case of monstrously tall Tucker Williams.

For this early on a Saturday, the class was surprisingly excited, zooming up on bikes and in their little used cars and chattering on the dock as they carelessly stripped down to their underwear to suit up, sprinkling the pier with an assortment of teenage garments. A few students helped Mr. Delaney ferry things down from the car, carefully storing them in the kayaks.

At 8:00, Mr. Delaney did a head count, and noticed that Amy Tilly seemed to be missing, but everyone else was present. He shrugged and slipped into the head kayak, and the rest of the students followed suit, rowing upriver with the tide with varying degrees of skill. The students had paired off, with each pair choosing a section of the river to supervise, and the first pair, Tucker and Cassandra, quickly got to work fanning out the kayaks, taking samples, and making notes on any fish they observed, taking photographs for reference.

This was the third time the class had gone out, and they seemed to be getting the hang of it, working in an efficient manner while still enjoying themselves. Jokes flew high over the sluggish water, and the harmony of the group was somewhat marvelous to Mr. Delaney, who had first taught a rougher bunch at inner city schools.

His students had grown up together, which meant that, as seniors, they’d been in school together for 13 years, and sometimes more, in the case of those who had gone to preschool. They knew each other inside and out, remembering everyone’s history, foibles, and attempts at reinventing themselves. Sometimes it seemed like they knew each other too well, knew perhaps a bit too much about each other and their families, but at the same time, it cut through the dance of acquaintance which seems to plague other schools at the beginning of the year. Much like the town itself, his students seemed almost like an anomaly; friendly, helpful, courteous people who did things like getting out of bed at seven in the morning to count fish.

Mr. Delaney was so calm and relaxed that he missed the undercurrents of tension in the group, which is perhaps understandable, because they were subtle. If Sara Harper and Kristin Ballantine had gotten into separate kayaks, despite the fact that the two girls were normally inseparable, Mr. Delaney didn’t notice. Amy’s partner, Paul Goodman, seemed undistressed by her absence, while his friend Clay Harper (Sara’s twin) was on edge, but no more so than usual. Mr. Delaney might have been forgiven for attributing the faint air of nerves and tension to end of the year nerves, and the cloud of uncertainty that always hangs over high school seniors in the spring.

The students broke for lunch at 11, pulling sandwiches and mysterious things in tupperware out of their bags and sitting companionably on a secluded beach they’d found the first time out. They talked, as people so often do, about nothing in particular, dabbling toes in the water and peeling off the upper halves of their wetsuits in the heat. Mr. Delaney noted a new bird for his life list, perched on a piling across the river, and with some reluctance prodded the students to get back to work after half an hour or so.

At 1, the students came across the first dead fish, floating glassy-eyed in the river. It was, Cassie noted, a fish which didn’t even belong in the river at all, but they duly photographed it, and Clay pointed out that there seemed to be a faint oil slick of some kind on the water, perhaps from a motorboat, and that was what had probably done the poor creature in.

When they rounded the oxbow at 1:40, therefore, they were unprepared for the sight which faced them: a veritable sea of dead fish, clogging the river and strangely emanating no scent, suggesting that their demise had been recent. Kristin even found one fish still jerking spasmodically. The oil slick was still present, looking glossy and sinister, suddenly, and Mr. Delaney realized that something, somewhere, must be deeply wrong.

This was about the time that James Farrier, with the Post, picked up a phone to ask a simple and perhaps career-making question.

“This data,” he said. “Can it be verified?”

Sara Harper vomited, profusely, into the river, and Mr. Delaney noted with clinical interest that she didn’t appear to have eaten lunch. Most of the other students turned various shades of green, not even bothering to tease Sara, and Clay paddled over with some water while everyone else floated, motionless, as though waiting for something to happen.

“Mr. Delaney?”

“Yes, Cassie?”

“Should we, ah, that is. I mean. Should we go back, now? Report this?”

“Yes, I suppose we should,” he said. “Would someone like to bag some samples?”

Tucker did so, and they paddled back swiftly, in silence.

Perhaps if the kayaks hadn’t been such a brilliant, eye-watering shade of orange, they would have noticed that the oil slick was clinging to the kayaks as well, leaving streamers behind in the water as the students paddled swiftly back to the pier. And perhaps, if the students hadn’t been so disconcerted, they might have realized that most of them had itchy fingers and toes, growing itchier by the minute. They also failed to notice the peculiar scent clinging around the pier, caused by the gently bobbing body of Amy Tilly.