I’d met a few river gods in my time. They tended to be cranky and unfriendly, and they thought of demigods as just another form of pollution, like old tires or cigarette butts.

“If he finds out I gave you directions,” Eudora muttered, almost to herself, “he’ll never let me into his yoga class again.”

“His yoga...? Actually, never mind,” I said. “You’re telling me you know where I can find him?”

Eudora looked at her watch. “Almost the end of the school day. I suppose if you were to simply wind up at the Elisson’s headwaters by accident, that wouldn’t be my fault.”

The tiles started to bubble and leak around my chair.

“No,” I said.

“Good luck, Percy!”

And she flushed me right through the floor.

I could have ended up in Greece or Brazil or who knows how far away. I was fortunate that I ended up in Yonkers, instead—which is the first time in history the wordsfortunateandYonkershave been used in the same sentence.

Okay, sorry, Yonkers, that’s not fair, but hey... it wasn’t a place I wanted to get flushed to right after school, knowing I’d have to take an extra thirty-minute train ride to get back to Manhattan.

My blue plastic chair and I shot out of a drainage pipe, tumbled down a rocky slope, and splashed into a creek. I sat there for a second, dazed and bruised, cold water soaking into my pants. The first thing I noticed was the bottom of my overturned chair, where a metal plate was inscribed:

IF FOUND, PLEASE RETURN TO EUDORA, ATLANTIC OCEAN

REFUNDABLE DEPOSIT: ONE GOLDEN DRACHMA

Great. If I failed to get into college or get a job, I could just wander around New York looking for blue plastic chairs to cash in for drachmas.

I struggled to my feet. The creek meandered through the middle of a gritty small-town business district: low brick buildings, old factories and warehouses repurposed as condos or offices. I knew it was Yonkers because along the riverfront, iron lampposts were hung with weirdly festive banners that yelledYONKERS!

It was the kind of post-industrial area that would’ve looked better in the dead of winter, under a heavy gray sky and a covering of dirty urban snow. Rough. Grim. ADeal with it or go homekind of place.

The riverbed was lined with scrubby bushes and gray boulders—many of them now painted with Percy blood and skin samples from my tumble out of the drainage pipe. The water was what you might politely callnon-potable—muddy brown and streaked with foam like bubble bath, except I was pretty sure it wasn’t bubble bath.

I had landed right next to a marshy area labeledSAW MILL RIVER MUSKRAT HABITAT.

I saw zero muskrats. Being smart animals, they were probably vacationing in Miami.

The name Saw Mill River sounded vaguely familiar. I remembered something in the news from when I was little. My mom had read me this article about how a bunch of urban rivers had been paved over back in the day and turned into underground drainage canals, and how people were now trying to open them up again and make them nature habitats. What did they call it...?Daylightinga river.

From what I could see, the Saw Mill River didn’t enjoy its daylighting much. Three blocks north, the water trickled reluctantly from a tunnel large enough to drive a truck through. The current was sluggish, as if it wanted to crawl back into the darkness and hide.

I wondered if Eudora had made a mistake.

Oh, you wanted the Elisson, the cleanest waters in the world?I imagined her saying.Sorry, I thought you said the Saw Mill, the cleanest waters in Westchester County! I always get those confused!

Or maybe she’d intentionally flushed me off-course to protect the Elisson’s location. If so, the river god must run a really great yoga class.

I waded upstream, slipping and stumbling over mossy rocks. My head was swiveling for monsters, or Yonkers police, or ill-tempered muskrats, but no one bothered me. About halfway to the tunnel, I caught my first whiff of putrid air from the entrance, like the breath of a sleeping giant who’d been living off moldy fish sandwiches. I doubled over and gagged.

The smell did not make me think of the cleanest waters in the world.

While I was hunched over, praying to the god of not vomiting, something floated by my foot. At first I thought it was a ripped grocery bag: just a shred of milky translucent plastic. Then I noticed the honeycomb pattern on the membrane. Like scales. Like the shed skin of a snake.

That was super helpful for my nausea.

Okay... Iris had told us that serpents bathed in the River Elisson. Maybe the water here was not so clean because I was wading through monster bathwater drain-off. Or that snakeskin could be from a normal snake, because nature.

I took a few more steps.