It cut a three-foot gash in the plastic, and that was all it took. The water pressure did the rest.

Crrrr-ACCCKK!

FWOOOOOOSSHH!

The water poured in like Niagara Falls.

"TWOOOOOSH!

A wave hit me and knocked my legs out from under me. The water picked me up and rocketed me down that Plexiglas tunnel. I went one way, everyone else was blown the other direction.

I saw the captain just ahead of me. I hit him with my feet, doing about fifty miles an hour. He went down and the water rushed over him.

"Jake! Rachel!" I yelled. But no one answered.

Then I couldn't yell anything anymore. The water swept over me, filling the tunnel completely. I fought my way to the top of the tunnel and tried to suck up a big, squirmy, silver air bubble I saw. I got a mouthful of saltwater instead.

Morph, you idiot! I told myself. I needed to go dolphin. No! Not dolphin. Dolphin needed to be able to reach the surface to breathe. I needed a fish. Long ago we had morphed trout. Could I still retrieve that morph?

All this time I was still shooting along, carried by the rushing water.

And then I realized I wasn't alone. There were fish with me. Big fish, little fish. All swimming around me.

Air! I needed air!

Bump! Something hit me. It brushed by me, spinning me around in the water. A body? One of the others? I spun around in the water. And, seeing me move, the shark came back toward me.

I yelped in fear and gave up bubbles of precious air from my lungs. I shot my arms out and kicked my legs hard and backpedaled through the water.

Morph a fish? The shark could eat either one of us!

I began swimming. I had to get back to the break in the tunnel. The hole Ax had made. If I could get through that, I could reach the surface.

Air! Air! My lungs were on fire! I could feel my throat spazzing as my lungs fought to fill themselves.

I swam down that tunnel with the shark following lazily behind.

Is it possible to sweat underwater? I felt like it was. My guts were jelly. My limbs were weak with fear, cramping up from lack of oxygen.

No time to morph. Only time to flee.

There! Was that the hole? Yes! It was a hole. A hole in the tunnel. No, wait. This hole was too round. Too perfectly round.

No time to worry. I kicked hard and started up through the vertical hole. Suddenly my head broke the surface. Air! I sucked it down and spewed it out and sucked it down again, making gasping, sobbing sounds.

Where was I? I was in a sort of vertical tunnel. It was no more than three feet wide. It extended above me for another five or six feet. And at the top there was a metal grill.

"The air-conditioning," I gasped. My voice rang flat and hollow. I was in an air-conditioning vent. This was how they ventilated the tunnel.

But I couldn't reach the grill overhead. And I was still treading water.

The shark! I stuck my face back in the water and opened my eyes to look.

I swear I nearly levitated. The shark was rising toward me like some kind of submarine-launched missile. I didn't think, I just reacted. I slammed my feet against one side of the shaft, my hands against the other, and I pressure-walked my way up and out of the water.

My butt was still in the water when I saw that hideous face poke up to take a look at me. That hideous, hammerhead face, with its dead eyes at the end of each side.

That got me up another foot. But the plastic was slippery. And I was too weak to keep it up for long.

"Go kill something else, you monster!" I yelled at the shark.

The head disappeared beneath the water. But I knew in my heart it was still there. Still waiting.

"Ahhh! Ahhh!" My left hand slipped and almost lost it. There was no way this could last. I'd fall. Sooner, not later.

Only one thing to do. I had to acquire that shark.

Animals go limp when you acquire them, I told myself. Except when they don't. Like Tobias's dolphin.

This was insane! I couldn't hold on. And if I dropped, my only hope was in actually grabbing hold of a hammerhead shark.

The shark poked his snout above the water again. It was now or never.

"If it turns out you eat me," I told the shark, "make it quick."

I released my pressure. And I dropped. Directly onto the shark.

It turns out, as tough as sharks are, they still aren't used to having screaming, flailing, panic-stricken human beings dropped on them from the sky.

Pah-LOOOSH!

I hit the shark and knocked him downward through the water. The two of us sank together, back into the main tunnel.

Before the shark could recover its wits, I shot out my hand and I grabbed him by the dorsal fin, and I thought, Please, please, I'm begging you, be like a normal animal and go limp!

I focused my mind. And to my infinite, profound, world-embracing relief, the hammerhead became peaceful and sluggish.

I wrapped my arms around the big monster, happy I'd worn long sleeves, and we floated up through the gash Ax had made. Up toward air and the stars and freedom.

He was still in an acquisition trance by the time my head broke the surface. We were in one of the tanks. The walls around were higher than they should have been, since the water had drained out to flood the tunnels. But up around the lip of the tank I saw anxious faces staring down.

"Hey. What are you guys up to?" I asked.

"Marco! You're alive!" Cassie said.

"Yeah. And I brought someone for each of you to meet. Dive on in. It's hammerhead time."

the next day there was a huge headline in the newspaper. A terrible accident at the Ocean World Aquarium. Two guards were missing. Also several fish.

The one guard who did remain told a bizarre tale of a half-deer, half-human creature. The aquarium spokesman sort of implied that the guards must have gotten drunk and shot up the place, causing the tunnel to shatter.

It was on the TV news and everything. CNN even sent a camera crew.

On Monday I handed in five pages of pure, total babble as a book report.

I wrote it on the bus. On Thursday I got it back. D-minus. The teacher wrote, "Nice try, Marco. Do it over, and this time try reading the book."