You know you're in for excitement when a fellow tells you to meet him at dusk in a fast boat, wear dark clothes and bring a good anchor and 150 feet of line.

These were Mack Lloyd's instructions, and the promise that went along was a load of rockfish -- legal ones, at that.

Rock are the troubled state fish of Maryland, which has banned all catching and possession. But in the Potomac River, which operates under separate jurisdiction, fishermen still may keep five rock a day over 18 inches. And in Washington's portion of the Potomac, you still may keep all you want, any size.

It was Washington waters we were headed to, for an adventure in the dead of night.

"The later it gets, the better it gets," said Lloyd, who, with his regular fishing partners, had caught more than 40 rockfish three nights in the preceding week, fishing into the wee hours of the morning.

"I use a canoe," he said, "but we'll be better off in your boat because people won't recognize us. I've been having a hard time shaking the crowds. They come looking for me."

Lloyd is a 37-year-old electrical contractor, and has fished, hunted and trapped the Potomac around his native Alexandria much of his life, having learned much of what he knows from his grandfather and father. "There isn't a better river in the world," he said.

We put in at the Park Service ramp just north of National Airport and nosed the skiff downstream as the sun set over Virginia.

It was a gorgeous evening, clear and cool, not a cloud in the sky. But Lloyd, like any good fishermen, saw doom. "I like it hot and muggy and still," he said nervously. "This breeze is going to hurt us. And the moon's up. I don't like that. Too much light could ruin it."

A half-moon was two-thirds of the way through its east-west journey. Jets were streaming noisily into National. A gentle chop stirred the water.

"You can go slow. We're just biding time," Lloyd said. "It won't get good until later." He guided a tour of his piece of the river, pointing out where islands once stood, since denuded for gravel; where marshes once were, where a chemical plant used to stand in Alexandria, which in his view is "turning into another Georgetown."

We slid past Smoot's Bay on the Maryland side, a miraculously wild place within sight of the Washington Monument where developers plan to build an eye-assaulting multimillion-dollar high-rise complex that belongs on K Street.

It was dark.

A buoy marking an eel pot streamed upriver, signifying that the tide had begun to flood.

"Let's go on up the river," Lloyd said. "There's a place where we might catch a few three- or four-pounders on this tide. It's dark enough now."

In District waters, we anchored at a place where the tide rolled over an old rockpile. He killed the running lights. "Shh," Lloyd said. "Just wait."

Shortly, life resumed on the rockpile. Rockfish began busting bait on the surface. You could hear the "slap" and "pop" of the strikes and see the water splash. Lloyd tossed a white plastic worm across the bar and retrieved it slowly. Nothing for a while. Then his fishing rod jerked sharply. Fish on.

"Nice one," said Lloyd. It was pulling four-pound line from his reel. The rod bent double and line ripped off. He worked the fish slowly and we got it into the net. Four-pounder.

"What'd I tell you?"

At about 11 p.m., Lloyd suggested we move downriver to his hot spot, where he expected the rock to be thick, but smaller. He took the wheel and piloted the boat through the darkness, along gravel bars and through stands of thick grasses, lights out so no one would follow.

The fish were breaking.

"Hear that 'pop' sound?" he said. "That's rockfish busting alewives."

We cast into the night, into the warm Potomac, and the rockfish started hitting. It was wonderful -- the kind of night rockfishing you read about in magazines, but rarely expect to encounter, least of all in your own backyard.

Lloyd thought it stunk. "We should be getting 10 times as many hits," he said. "The boat must be scaring them. The canoe sits lower in the water."

We moved a few times. It kept being great and he kept complaining. We turned several fish loose and kept seven of the larger ones to eat.

Just before 2 a.m. we fired up the big Mercury and turned for home. The lights of Washington beckoned. The breeze was cool, invigorating, as we skimmed along dappled black water.

Beautiful night. Beautiful city. Beautiful world.