“Shhhh!” Shelly pointed toward a white pickup that was rolling into the lot.

The truck pulled up and parked near the Jeep. Stamped on the door of the cab was: DEPARTMENT OF PARKS AND RECREATION.

A man in a tan uniform got out and gave us a friendly nod. From the bed of the pickup he removed a small sledgehammer, a half dozen metal posts, and a stack of cardboard signs.

“You folks on your way to the beach?” he asked.

“What's up?” said Shelly.

The man showed us one of the signs. DANGER, it warned in big letters. BEWARE OF CONTAMINATED WATER.

Beneath those words, in smaller red lettering, it said: SWIM AT YOUR OWN RISK.

“Contaminated with what?” asked my sister, acting as if she didn't know.

“Human waste,” said the man from Parks and Recreation. “We got a call from a guy who was fishing out here this morning. The health department came and sampled the water-it tested off the charts. You all might want to try Long Key, or maybe Harris Park.”

“Sounds like a plan,” Shelly said, playing along.

After the man went off to post the warning signs, my sister and I said goodbye to Shelly and began walking to our bikes.

“Noah, what you did back there for that sea turtle, that was very…”

“Dumb? I know.”

“No. Cool,” Abbey said, “in a really twisted way.”

“Thanks, I guess.”

“We can't give up on this,” she added grimly.

“Now you sound like Dad.”

“Well? You're the one who went into that scuzzy water-twice! Doesn't it make you furious?”

“Yeah, it does.”

Furious and sick at the same time. But I thought of Abbey's spying mission the night before, and what a disaster it could have been. I'd never forget the cold-blooded look in Luno's eyes when he saw us standing in Dusty's ticket shack.

“Mom doesn't need any more excitement from us,” I told my sister.

“She won't have to know a darn thing,” Abbey said, “because next time we'll do it right.”

The “we” was a given. I wasn't about to let my sister go anywhere near that marina again without me.

We unlocked our bikes and started pedaling home in the thick July heat. I knew I stunk from the crappy water, but Abbey claimed she didn't smell a thing. I kept thinking about how easy it was for Dusty Muleman to get away with what he was doing. With so many big boats on the water, nobody had been able to trace the pollution along Thunder Beach directly to the Coral Queen.

Or maybe nobody had tried hard enough.

It was time that somebody did.

“We can't get Dad involved in this, either,” I said to Abbey. “He's had enough trouble already.”

“Definitely.” She grinned. “Noah, does this mean you've got a plan?”

“Don't get carried away,” I said, which ought to be the Underwood family motto.

Dad was serious about getting serious.

The same morning he was released from jail, he went out and got himself hired by a company called Tropical Rescue. It wasn't the sort of work that my father could put his heart into, but I knew why he took the job.

It was the boat.

They let him use a twenty-four-foot outboard with a T-top and twin 150s-not for fishing but for towing in tourists who ran out of gas or rammed their boats aground.

Normally my father has no patience for these sorts of bumblers. He calls them “googans” or even worse, depending on what kind of fix they've gotten themselves into. But Dad needed the job, so he buttoned his lip and kept his opinions to himself.

Unless it's a life-or-death emergency, the Coast Guard refers disabled-boat calls to private contractors like Tropical Rescue, which charge big bucks. They stay busy, too. It's amazing how many people are too lazy to read a fuel gauge, a compass, or a marine chart. They just point their boats at the horizon and go. All around the Keys you can see their propeller trenches-long ugly gouges, like giant fingernail scrapes, across the tidal banks. It takes years for the sea grass to grow back.

Dad's first rescue job was a boatload of software salesmen from Orlando who were stranded all the way out at Ninemile Bank. Somehow they'd managed to beach a brand-new Bayliner on a flat that was only four inches deep. That's not easy to do, unless you're bombed or wearing a blindfold.

Miraculously, Dad restrained himself from saying anything insulting. He didn't get mad. He didn't make fun of the bonehead who'd been driving the boat.

No, my father-the new and improved Paine Underwood-stayed calm and polite. He waited patiently for the tide to come up, tugged the Bayliner off the bank, and towed it back to Caloosa Cove. He told us he almost felt sorry for the software salesmen when he handed them the bill, which didn't even include the hefty fine from the park service for trashing the sea grass. It was probably one of the most expensive vacations those guys ever had.

Even though Dad didn't like dealing with googans, he was ten times happier on the water than he was driving a taxi. That meant Mom was in a better mood, too, laughing and kidding around the way she used to do.

The two of them were getting along so well that Abbey and I were extra careful not to mention the sticky subject of Dusty Muleman's casino boat. We discussed our new plan of attack only when we were alone and away from the house, where our parents couldn't hear us.

A couple of days after my father got out of jail, the Parks Department took down the pollution warnings at Thunder Beach. The next morning, Abbey and I put on our bathing suits and grabbed a couple of towels and dashed outside. Mom and Dad figured we were heading for the park, which is exactly what we wanted them to think.

Because we were really going to Shelly's trailer.

I had to knock a half dozen times. When she finally came to the door, she didn't seem especially delighted to see us. Her eyes were puffy and half closed, and it looked like somebody had set off a firecracker in her hair.

“Time izzit?” she asked hoarsely.

“Seven-thirty,” I said.

She winced. “A.M.? You gotta be kiddin' me.”

Abbey said, “It's important. Please?”

We followed Shelly inside. She sagged onto the sofa and tucked her legs up under her tatty pink bathrobe.

“Killer headache,” she explained, running her tongue across her front teeth. “Large party last night.”

She was clearly in pain, so we got straight to the point. “We need your help,” I said, “now.”

“To do what?”

“To stop Dusty Muleman. You promised, remember?”

She laughed-one of those tired, what-was-I-thinking laughs. She looked across at Abbey. “And you promised to keep your big brother outta trouble.”

“We won't get in any trouble,” Abbey said evenly, “if you help us.”

It sounded like Shelly was having second thoughts. I wondered if she really was afraid of Dusty Muleman after all.

In a discouraged voice she said, “I don't know what we can do to stop him. He's tight with all the big shots in town.”

“But he's poisoning Thunder Beach,” I said. “You know how sick a kid could get from swimming in that bad water? Same goes for the fish and the dolphins and the baby turtles. It sucks, what Dusty is doing. It's awful.”

“Yeah, but-”

“And don't forget what happened to Lice,” I added. “Remember how you told me you had a dog in this fight? Remember-”

“Lice is exactly what I been thinkin' about,” Shelly cut in. “Say they really killed him, okay? You s'pose they'd hesitate to do the same to me or you, if somethin' goes wrong?”

It was about time she got worried, and who could blame her? If she was right about Lice being dead, then Dusty and Luno were cold-blooded murderers.

But one glance and I knew Abbey wouldn't back off, no matter what the risks. Neither could I.

“Shelly, I know it's dangerous-”