I jumped and landed on a rock island in the middle of the otter exhibit. I willed a column of water out of the pond and doused the horses, temporarily extinguishing their flames and sending them into confusion. The otters weren’t happy with me. They chattered and barked, and I figured I’d better get off their island quick, before I had crazed sea mammals after me too.

I ran as Phobos cursed and tried to get his horses under control. Clarisse took the opportunity to jump on Deimos’s back just as he was lifting his javelin. Both of them went tumbling out of the chariot as it lurched forward.

I could hear Deimos and Clarisse starting to fight, sword on sword, but I didn’t have time to worry about it because Phobos was riding after me again. I sprinted towards the aquarium with the chariot right behind me.

‘Hey, Percy!’ Phobos taunted. ‘I’ve got something for you!’

I glanced back and saw the chariot melting, the horses turning to steel and folding into each other like clay figures being crumpled. The chariot refashioned itself into a black metal box with caterpillar tracks, a turret and a long gun barrel. A tank. I recognized it from this research report I’d had to do for history class. Phobos was grinning at me from the top of a World War II panzer.

‘Say cheese!’ he said.

I rolled to one side as the gun fired.

KA-BOOOOM! A souvenir kiosk exploded, sending fuzzy animals and plastic cups and disposable cameras in every direction. As Phobos re-aimed his gun, I got to my feet and dived into the aquarium.

I wanted to surround myself with water. That always increased my power. Besides, it was possible Phobos couldn’t fit the chariot through the doorway. Of course, if he blasted through it, that wouldn’t help…

I ran through the rooms washed in weird blue light from the fish tank exhibits. Cuttlefish, clown fish and eels all stared at me as I raced past. I could hear their little minds whispering, Son of the sea god! Son of the sea god! It’s great when you’re a celebrity to squids.

I stopped at the back of the aquarium and listened. I heard nothing. And then… Vroom, Vroom. A different kind of engine.

I watched in disbelief as Phobos came riding through the aquarium on a Harley-Davidson. I’d seen this motorcycle before: its black flame-decorated engine, its shotgun holsters, its leather seat that looked like human skin. This was the same motorcycle Ares had ridden when I’d first met him, but it had never occurred to me that it was just another form of his war chariot.

‘Hello, loser,’ Phobos said, pulling a huge sword out of its sheath. ‘Time to be scared.’

I raised my own sword, determined to face him, but then Phobos’s eyes glowed brighter, and I made the mistake of looking into them.

Suddenly I was in a different place. I was at Camp Half-Blood, my favourite place in the world, and it was in flames. The woods were on fire. The cabins were smoking. The dining pavilion’s Greek columns had crumbled and the Big House was a smouldering ruin. My friends were on their knees pleading with me. Annabeth, Grover, all the other campers.

Save us, Percy! they wailed. Make the choice!

I stood paralysed. This was the moment I had always dreaded: the prophecy that was supposed to come about when I was sixteen. I would make a choice that would save or destroy Mount Olympus.

Now the moment was here, and I had no idea what to do. The camp was burning. My friends looked at me, begging for help. My heart pounded. I couldn’t move. What if I did the wrong thing?

Then I heard the voices of the aquarium fish: Son of the sea god! Wake!

Suddenly I felt the power of the ocean all around me again, hundreds of litres of salt water, thousands of fish trying to get my attention. I wasn’t at camp. This was an illusion. Phobos was showing me my deepest fear.

I blinked and saw Phobos’s blade coming down towards my head. I raised Riptide and blocked the blow just before it cut me in two.

I counterattacked and stabbed Phobos in the arm. Golden ichor, the blood of the gods, soaked through his shirt.

Phobos growled and slashed at me. I parried easily. Without his power of fear, Phobos was nothing. He wasn’t even a decent fighter. I pressed him back, swiped at his face, and gave him a cut across the cheek. The angrier he was, the clumsier he got. I couldn’t kill him. He was immortal. But you wouldn’t have known that from his expression. The fear god looked afraid.

Finally I kicked him backwards against the water fountain. His sword skittered into the ladies room. I grabbed the straps of his armour and pulled him up to face me.

‘You’re going to disappear now,’ I told him. ‘You’re going to stay out of Clarisse’s way. And if I see you again, I’m going to give you a bigger scar in a much more painful place!’

He gulped. ‘There will be a next time, Jackson!’

And he dissolved into yellow vapour.

I turned towards the fish exhibits. ‘Thanks, guys.’

Then I looked at Ares’s motorcycle. I’d never ridden an all-powerful Harley-Davidson war chariot before, but how hard could it be? I hopped on, started the ignition, and rode out of the aquarium to help Clarisse.

I had no trouble finding her. I just followed the path of destruction. Fences were knocked down. Animals were running free. Badgers and lemurs were checking out the popcorn machine. A fat-looking leopard was lounging on a park bench with a bunch of pigeon feathers around him.

I parked the motorcycle next to the petting zoo, and there were Deimos and Clarisse in the goat area. Clarisse was on her knees. I ran forward but stopped suddenly when I saw how Deimos had changed form. He was Ares now – the tall god of war, dressed in black leather and sunglasses, his whole body smoking with anger as he raised his fist over Clarisse.

‘You failed me again!’ the war god bellowed. ‘I told you what would happen!’

He tried to strike her, but Clarisse scrambled away, shrieking, ‘No! Please!’

‘Foolish girl!’

‘Clarisse!’ I yelled. ‘It’s an illusion. Stand up to him!’

Deimos’s form flickered. ‘I am Ares!’ he insisted. ‘And you are a worthless girl! I knew you would fail me. Now you will suffer my wrath.’

I wanted to charge in and fight Deimos, but somehow I knew it wouldn’t help. Clarisse had to do it. This was her worst fear. She had to overcome it for herself.

‘Clarisse!’ I said. She glanced over, and I tried to hold her eyes. ‘Stand up to him!’ I said. ‘He’s all talk. Get up!’

‘I… I can’t.’

‘Yes, you can. You’re a warrior. Get up!’

She hesitated. Then she began to stand.

‘What are you doing?’ Ares bellowed. ‘Grovel for mercy, girl!’

Clarisse took a shaky breath. Very quietly, she said, ‘No.’

‘WHAT?’

She raised her sword. ‘I’m tired of being scared of you.’

Deimos struck, but Clarisse deflected the blow. She staggered but didn’t fall.

‘You’re not Ares,’ Clarisse said. ‘You’re not even a good fighter.’

Deimos growled in frustration. When he struck again, Clarisse was ready. She disarmed him and stabbed him in the shoulder – not deep, but enough to hurt even a godling.

He yowled in pain and began to glow.

‘Look away!’ I told Clarisse.

We averted our eyes as Deimos exploded into golden light – his true godly form – and disappeared.

We were alone except for the petting zoo goats, which were tugging at our clothes, looking for snacks.

The motorcycle had turned back into a horse-drawn chariot.

Clarisse looked at me cautiously. She wiped the straw and sweat off her face. ‘You didn’t see that. You didn’t see any of that.’

I grinned. ‘You were great.’

She glanced at the sky, which was turning red behind the trees.

‘Get in the chariot,’ Clarisse said. ‘We’ve still got a long ride to make.’

A few minutes later we reached the Staten Island Ferry and remembered something obvious: we were on an island. The ferry didn’t take cars. Or chariots. Or motorcycles.

‘Great,’ Clarisse mumbled. ‘What do we do now? Ride this thing across the Verrazano Bridge?’

We both knew there wasn’t time. There were bridges to Brooklyn and New Jersey, but either way it would take hours to drive the chariot back to Manhattan, even if we could fool people into thinking it was a regular car.

Then I got an idea. ‘We’ll take the direct route.’

Clarisse frowned. ‘What do you mean?’

I closed my eyes and began to concentrate. ‘Drive straight ahead. Go!’

Clarisse was so desperate she didn’t hesitate. She yelled, ‘Hiya!’ and lashed the horses. They charged straight towards the water. I imagined the sea turning solid, the waves becoming a firm surface all the way to Manhattan. The war chariot hit the surf, the horses’ fiery breath smoking all around us, and we rode the tops of the waves straight across New York Harbor.

We arrived at Pier 86 just as the sunset was fading to purple. The USS Intrepid, temple of Ares, was a huge wall of grey metal in front of us, the flight deck dotted with fighter aircraft and helicopters. We parked the chariot on the ramp and I jumped out. For once I was glad to be on dry land. Concentrating on keeping the chariot above the waves had been one of the hardest things I’d ever done. I was exhausted.

‘I’d better get out of here before Ares arrives,’ I said.

Clarisse nodded. ‘He’d probably kill you on sight.’

‘Congratulations,’ I said. ‘I guess you passed your driving test.’

She wrapped the reins around her hand. ‘About what you saw, Percy. What I was afraid of, I mean –’

‘I won’t tell anybody.’

She looked at me uncomfortably. ‘Did Phobos scare you?’

‘Yeah. I saw the camp in flames. I saw my friends all pleading for my help and I didn’t know what to do. For a second, I couldn’t move. I was paralysed. I know how you felt.’

She lowered her eyes. ‘I, uh… I guess I should say…’ The words seemed to stick in her throat. I wasn’t sure Clarisse had ever said thank you in her life.

‘Don’t mention it,’ I told her.

I started to walk away, but she called out, ‘Percy?’

‘Yeah?’

‘When you, uh, had that vision about your friends…’

‘You were one of them,’ I promised. ‘Just don’t tell anybody, okay? Or I’d have to kill you.’

A faint smile flickered across her face. ‘See you later.’

‘See you.’

I headed off towards the subway. It had been a long day, and I was ready to go home.

Interview with

PERCY JACKSON,

Son of Poseidon

What’s your favourite part about summers at Camp Half-Blood?

Percy: Seeing my friends, for sure. It’s so cool to come back to camp after a year at school. It’s like coming home. The first day of summer, I’ll walk down to the cabins and Connor and Travis are stealing stuff from the camp store, and Silena is arguing with Annabeth trying to give her a makeover, and Clarisse is still sticking the new kids’ heads into the toilets. It’s nice that some things never change.