I saw round glass portholes in front, back, and on both sides. Two big headlights in front. Twin thrusters at the back.

  “The three of us should fit okay,” Dr. D said. “It’ll be a snug ride. My little sub won’t go long distances. But it’ll take us down to the sunken ship — if we find it. And it has a little speed. I can get it up to five knots if I really push it.”

  Another dangerous mission for the Undersea Mutant! I thought.

  I imagined myself in a furious sword fight with a zombie pirate. Then I saw myself swimming away in victory, pulling a huge treasure chest brimming with jewels behind me.

  Actually, I felt a little shaky. I had a fluttering feeling in my stomach. I couldn’t help it. I was scared. The Deep Diver looked so small and fragile.

  I imagined it being swallowed by an enormous shark. Then I shut my eyes and I imagined a deafening crash. Shattered glass. I pictured a GREAT GREEN EEL crashing through a porthole!

  It had me in its teeth! It wrapped its tongue around me. I was about to become eel food!

  WHOA! BILLY — STOP!

  Yes, I could dream up crazy adventures all day long.

  But even with my great imagination, I couldn’t dream up the real horrors that awaited us at the bottom of the ocean.

  It all started the next afternoon.

  A little after two o’clock, Dr. D called Sheena and me into his computer lab on the main deck of the Cassandra. “I think we’re very close,” he said.

  He was staring at four monitors. They had blue and green ocean maps on them. White dots moved across the screens.

  He pointed to a white dot on the top screen. “That’s us,” he said. Then he moved his finger over a dark shape at the bottom of the screen. “That could be the sunken ship.”

  Sheena and I stared at the dark shape. It didn’t look like a ship. It just looked like a black smudge on the screen.

  Dr. D tapped the smudge two or three times. Then he jumped up from his chair. “Let’s go check it out!”

  I swallowed hard. “You mean — get in the sub?”

  Sheena pumped her fists in the air. “This is totally cool!” she cried.

  I couldn’t let her see how scared I was. I slapped her a high five. “Don’t be scared, Sheena. Dr. D and I can handle things.”

  “Funny,” Sheena said, rolling her eyes. “That’s about as funny as a shark bite.”

  I bit her arm. Not too hard. Just as a joke. She’s so annoying.

  When we came out on the deck, Dr. D had already anchored the Cassandra. It was a bright day with puffy white clouds high in the sky. The blue-green waves lapped calmly at our boat.

  Dr. D led us to the little sub. He pulled open the hatch. We peered down into the small chamber.

  “Lower yourself slowly,” Dr. D said. “There’s plenty of room once you get in the cabin.”

  Sheena bumped me out of the way. “Ladies first,” she said. She squeezed into the hatch and lowered herself quickly out of sight.

  “Awesome!” her voice echoed up from the tiny chamber.

  My turn.

  The Undersea Mutant follows the call to adventure! I told myself. Wherever danger goes, the Mutant follows!

  My foot missed the bottom ladder rung. I fell. Landed on my feet. “Ta da!” I made it look as if I meant to do it.

  Sheena didn’t see my klutzy move. She took the seat at the end and studied the control panel. She turned and grinned at me. “What do you think would happen if I pushed this button?”

  “Sheena — don’t!” I cried.

  She laughed. “Just testing you. You failed.”

  What a pain. Always trying to prove that she’s braver than me.

  I dropped down next to her. The black plastic seats were jammed close together. The cabin ceiling was just a few inches over our heads.

  I heard the hatch slam shut above us. Dr. D lowered himself into the cabin and dropped into the seat next to me.

  He leaned over the control panel. He threw a few switches. The cabin filled with orange light. He pushed a yellow button, and the engine hummed to life.

  “This sub is so easy to pilot, a monkey could do it,” he said.

  “Does that mean Billy could do it, too?” Sheena cracked.

  “Let me show you both,” Dr. D said. “This is the helm. It steers just like the wheel of a car. That yellow button is the ignition.”

  He tapped a round screen on the control panel. “That’s the satellite navigation system,” he said. “It’s like the GPS navigation in a car — only it maps the ocean. And this screen next to it is the sonar echo display. It picks up any objects on the ocean floor.”

  He pointed down to his foot. “See the pedal? It looks like a gas pedal, right? Push the top of it down with the ball of your foot and the sub goes forward. Push the bottom down with your heel and the rear thrusters come on, sending the sub back.”

  He grabbed the stick to the right of the wheel. “Pull up and the sub goes up. Pull down and we descend.”

  I swallowed hard. I felt a little seasick, and we weren’t even underwater yet.

  I won’t be so stressed once we start moving, I told myself.

  What would the Undersea Mutant do in this situation?

  I was too excited and scared to think about the Undersea Mutant. “D-do you really think the pirate ship is down here?” I stammered.

  Dr. D studied the satellite navigation screen. “Let’s find out, Billy,” he murmured.

  He lowered his foot on the accelerator and pulled the stick down. I heard the thrusters roar to life. I grabbed the sides of the seat as we splashed hard in the water.

  We were sinking slowly. I stared out the porthole. The blue sky disappeared as water covered the glass.

  Down. Down.

  A string of bubbles rippled outside the glass. The water darkened as we dropped. Dr. D pushed a switch, and the orange lights inside our chamber brightened to yellow.

  “My ears just popped,” Dr. D said. “How about yours?”

  “I think my eyes just popped!” I said. I wanted it to sound like a joke. But I think I sounded a little scared.

  “Do we have diving equipment?” Sheena asked. “If we find the ship, can we swim out and explore it?”

  What a show-off! I thought. She wants to swim at the bottom of the ocean?

  Dr. D shook his head. “No room for diving equipment. If the pressure holds, we should be able to get very close to the sunken ship. We can see a lot from inside here.”

  If the pressure holds?

  An hour passed. Then another hour. “We have to descend very slowly,” Dr. D explained. “Especially in this tiny tin can.”

  I wished he wouldn’t call it a tin can. I gazed out at the twin beams of light. All I could see was the blue-green murk.

  Finally, Dr. D pulled the stick up and cut off the rear thrusters. We slowly stopped dropping. The sub rocked from side to side.

  Dr. D squinted at the monitor. “We’re about a hundred yards from the ocean floor,” he said. “Need to move forward now.”

  I saw strange black coral formations out the side porthole. Shadowy forms. Like underwater ghosts, I thought.

  Dr. D pressed the accelerator. The sub hesitated for a moment, then shot forward.

  He mopped sweat off his forehead with the palm of his hand. “I’m pretty excited,” he said, staring at the navigation screen. “I’ve studied all kinds of sea life. But I’ve never seen anything like this. I —”

  The engine sputtered. It sounded like a power lawn mower shutting down.

  “Whoa —” Dr. D uttered. “What’s going on?”

  Silence now.

  “No problem. It just stalled,” Dr. D said. He pushed the yellow ignition button.

  The engine coughed, sputtered. Died again.

  “Hey — !” I let out a cry as I saw a huge black cloud rolling through the water toward us.

  Sheena saw it, too. “What’s that?” she cried.

  It moved quickly. No time to speed out of i
ts way.

  I watched it roll forward, like an immense black tidal wave. Blacker than ink. Blacker than anything I’d ever seen.

  “Dr. D — ?” My voice came out in a choked whisper. I gripped the sides of the seat. I was panting so hard, I could barely breathe.

  “Dr. D — ?”

  The blackness swept into the sub. Icy cold. I couldn’t see Dr. D. I couldn’t see Sheena. I couldn’t see my own hands in front of me.

  “Dr. D?” I repeated in a tiny voice. “What is happening?”

  “I … I don’t know,” he answered. “And I don’t like it.”

  “I can’t see a thing,” Sheena said. “It’s like I’m blind!” She grabbed my arm. “Did we float into some kind of cave?”

  “No,” Dr. D replied. “We’re not in a cave. I’m not sure what this is.”

  “M-maybe it will float past us,” I choked out. I kept blinking, trying to see. I felt sick. I swallowed hard, trying not to gag.

  Sheena squeezed my arm. She was actually scared.

  “There are inky parts out in these deep waters,” Dr. D said. “But I’ve never seen anything like this. Let me get the thrusters going, and I’ll try to steer us out of it.”

  I couldn’t see him. But I heard him working the controls. He muttered to himself each time the engine sputtered and died.

  “Whoa!” I let out a cry as we started to spin.

  Sheena bumped hard against me.

  The sub spun faster — round and round — and I felt it start to drop.

  We whirled down, then back up, spinning faster.

  I felt dizzy. I grabbed my stomach. I could feel my lunch rise up to my throat.

  “I — I can’t explain this,” Dr. D stammered. “Something is pulling us. Something —”

  He stopped suddenly.

  The spinning slowed. The darkness covered us.

  I jumped and let out a frightened cry when I heard a loud noise close to me.

  THWUPPPPP.

  It sounded like when Dad opens a coffee can and the air pops out.

  Then … silence.

  I held my breath, struggling not to barf. Finally, the inky blackness started to lift.

  “Dr. D? Are we okay?” I asked in a shaky voice.

  No answer.

  Blinking, I struggled to see through the gray mist.

  “Dr. D? Uncle George? What’s happening?” I asked.

  “Can you get us back to the surface?” Sheena asked.

  The lights flashed back on.

  Sheena and I both let out shocked cries.

  Dr. D was gone!

  A cold shiver stiffened my back. I stared at the empty seat next to me.

  “NO! NO! It’s impossible!” I screamed.

  Sheena jerked her body around and looked up. “The hatch —” she murmured. “Is it open? Did he — ?”

  I jumped to my feet and pulled myself up to the hatch.

  Locked tight.

  “But — he couldn’t vanish into thin air!” Sheena said in a whisper. “Dr. D? Dr. D?” She began shouting his name. “Can you hear us?”

  Silence.

  The sub rocked gently. The black cloud had completely lifted.

  I slumped into Dr. D’s seat. Sheena and I stared at each other. I knew we were both thinking the same thing.

  “That pirate captain and his ship,” I said. “They disappeared in a black cloud — remember?”

  “No, Billy — don’t say that!” Sheena cried, grabbing my arm. “They were never seen again. Don’t say that! Don’t! We’ll find Dr. D. I know we will!”

  “Okay, okay,” I said. “Let go of me. You’re hurting me.”

  She didn’t even realize she kept squeezing my arm. “Billy, what are we going to do?”

  I didn’t answer. I gripped the wheel hard and tried to fight my panic.

  Here we were, suddenly all alone near the bottom of the ocean in this tiny submarine.

  How will we find Dr. D? How much air do we have? How do we get back to the Cassandra? Are all THREE of us going to disappear?

  Every question sent shiver after shiver down my back. I gripped the wheel tighter, struggling to think.

  Strong currents rocked us from side to side. The twin lights on the front couldn’t cut through the dark waters.

  “The radio!” I cried. “We can call for help.” I reached for the radio receiver.

  “Do you know how to work it?” Sheena asked in a tiny voice.

  “No,” I said. “But maybe I can figure it out.”

  I pushed the two buttons beneath the speaker. “Hello? Hello? Can anyone hear me?”

  Silence.

  “Hello?” I pushed more buttons. “Hello? Is anyone there?”

  Silence. I couldn’t even get any static.

  “We’re too far down,” I said. “The radio won’t work at this depth.”

  Sheena was hugging herself, trying to stay calm. “Well, get us back to the surface,” she snapped. “If we can get back to the Cassandra, we can radio for help.”

  I leaned over the control panel. My hand trembled as I pushed the yellow ignition button.

  “Hey!” To my surprise, the engine roared to life.

  “Yes!” Sheena cried. “We’ve got power! Bring us up, Billy! Hurry.”

  I pushed my foot down on the accelerator. I pushed the stick up all the way.

  “Whoa! What’s wrong?” I gasped.

  We nosed down hard.

  My head hit the glass. I saw flashing bursts of red. I let out a cry of pain.

  Sheena screamed.

  I pulled the stick down, then up again. But we kept falling. Faster. As if a strong force was sucking us down.

  “Pull us up! Pull us up!” Sheena cried, frantically slamming her hands on the control board.

  I stared into the beams of light in front of us. They were tilting down. “What is that?” I gasped.

  “I … I think it’s a ship!” Sheena cried. “A sunken ship! DO something, Billy! DO something! We’re going to CRASH right into it!”

  It was all happening too fast to think. The dark form of the sunken ship rose up in front of us.

  “Stop! Stop! Stop!” I didn’t even realize I was screaming the word over and over.

  A hard bounce sent me spilling forward. I hit the control panel.

  To my shock, the engine sputtered and died.

  Through the murky water, I stared down at the sunken ship, tilted nearly on its side on the ocean floor.

  I saw broken masts. Tattered sails covered in algae. A ragged hole the size of a car in the side of the bow.

  “It’s the pirate ship,” I said. “The Scarlet Skull. Sheena — do you believe it? We found it!”

  Staring straight ahead, Sheena tugged at her hair. “We’re still dropping,” she said. “You have to get us out of here. Can you do it?” She grabbed my arm.

  “M-maybe,” I whispered.

  I stared down at the ship’s deck, covered in barnacles. Brown and black coral and slimy green algae encrusted the walls. The ship’s wheel lay on its side, cracked and rotted.

  I pushed the ignition button. The engine sputtered but didn’t start. The dark water bubbled all around us — and the sub dropped sharply.

  “Oh, no! Oh, no!” I screamed. My head smacked the glass again as our sub hit the mossy deck of the old ship and bounced up.

  My hands flew off the controls. A strong current pushed us forward. We rammed into the main cabin wall.

  CRAAAAAACK!

  We both screamed in horror.

  Our sub just split open!

  We’re going to DROWN down here!

  But no.

  The sub was okay. Part of the ship’s wall splintered. It cracked and fell away.

  The sub floated into the ship. Into a vast cabin, seaweed clinging to the ceiling and walls. Hundreds of silvery fish — thin as needles — fed off the weeds.

  Silence inside the ship. Our sub tilted and spun slowly, casting a murky light all around.

  “I … I th
ink we’re trapped in here,” I whispered. “I don’t think we can get out.”

  I was totally losing it. I never admitted it, but I always counted on Sheena to be the brave one. But now, it was impossible to be brave. We were both terrified out of our skulls!

  As I peered out into the ship’s cabin, Sheena shoved me aside and grabbed the controls. “Get back, Billy. Let me try.”

  She pushed the ignition button once. Twice. The engine only coughed. She stamped down hard on the accelerator. And then froze.

  I saw her blue eyes bulge. I turned to follow her stare.

  We both screamed when we saw it.

  The face. The grinning face in the water. Staring in at us.

  I gaped in horror at the grinning skull. The top of its head was crusted with black crab shells and snails. Fat brown sea worms bulged inside its mouth and its empty eye sockets.

  It pressed against the glass in front of us. A skeleton in a rotting shirt and torn trousers. Its horrible face stared in at us. Then it raised its bony arms … clenched its bony fingers into two fists.

  BAM. BAM.

  I jumped as it punched the glass with both fists.

  “It … it’s ALIVE. It’s trying to break in,” Sheena said in a trembling whisper.

  BAM. BAM.

  I jumped with each punch.

  From somewhere deep in the sunken ship, I heard a low moan. Like an animal in pain. And then ugly moans all around us.

  And as we stared in openmouthed panic, a wall of skeletons floated up, pressing their skulls against the glass.

  Skeletons in tattered clothes, algae growing on their skulls, black crab shells hardened over their bones.

  Frozen in terror, I stared at the dark, empty eye sockets, their toothless grins, their cracked skulls, the worms and snails and crabs clinging to them.

  BAM. BAM.

  They lowered their skulls and smacked the glass with their foreheads. Again. Again.

  BAM. BAM.

  They hammered the glass with their skulls and their bony hands. I saw fingers break off and float away. But the grinning skeletons kept pounding … pounding.

  I whipped my head around and saw more of them behind us, clinging to the sub.