He turned and gestured at the submersible. “Some might even call me a pirate. But, I ask you, did a pirate ever have such wonderful machines?”

“Sir, I’ve never seen a submersible with arms,” Jackson said.

Ruby cocked an eyebrow. “You know about submersibles?”

“I’m not just a pretty face, you know,” Jackson said.

Blancard laughed. “You are right, my friend. Not a lot of submersibles have robotic limbs, but they are useful for picking things up off the ocean floor, and I have found that in the briny deep there are things lurking that might enjoy taking a bite out of you. Some of those things are very, very big. I had these arms designed so I could fight back. Allow me to introduce you all to your vessel, the Muhammad Ali. Floats like a butterfly but stings like a bee.”

He pushed a button on a control pad and the two mechanical arms went into action, shadowboxing the air, until coming to a rest.

“Awesome sauce!” Flinch cried.

“I call dibs on the fighting arms,” Matilda said.

“Yes, the Ali’s a fighter, and strong. Has a shell made from titanium and a Plexiglas window shield that can resist nearly a hundred times the pressure of the surface.”

“What’s the plan, boss?” Ruby asked Brand.

“I’ll leave that to our information specialist,” Brand said as he gestured to Ms. Holiday.

“We’re three miles above the wreck of the Bom Jesus, a Portuguese trading ship that is rumored to have sunk here two hundred and fifty years ago. Among its cargo were silk, spices, and three tons of Portuguese gold. We also believe that the hold contains the Azreal Diamond Cache. Legend has it that the ship was hauling crates of enormous diamonds—some of the biggest the world had ever seen. Miners discovered them on the Ivory Coast and it took a hundred men to get the entire haul aboard the ship,” Ms. Holiday said, then turned to Captain Blancard. “Most people believe the diamonds are a myth.”

“Most people have no imagination, Lisa,” Blancard said with a mighty laugh. “Which is exactly how my men and I have gotten so rich.”

Blancard’s sailors let out a loud “Boo-yah!”

Agent Brand turned to the children. “The idea here is to take the diamonds before Simon can. No diamonds, no doomsday device. The mission is a little different than most, but all of you have been trained in underwater combat, so it shouldn’t be too difficult. Take the Ali down to the ocean floor and find the shipwreck.”

“Do you think the diamonds are really down there?” Matilda asked.

“Eyewitness reports claim the ship was too heavy to maneuver,” Ms. Holiday noted. “It’s very likely that the extra weight of the jewels led to its sinking.”

“If they are down there, use the submersible to bring them to the surface,” Blancard said. “And keep the cameras running at all times. My crew’s eyes can spot things of value that you might overlook. That’s how we make our living.”

“So where are our packs?” Duncan asked the librarian.

“Kids, everything you need for this mission is up here,” she said as she tapped her finger against her skull.

“You’ve got to be—” Duncan cried, but caught Ruby’s stern expression reminding him that he was supposed to “man up.”

“None of your abilities would do you much good underwater, anyway, bro,” Flinch said.

“Blancard will use the radio to guide you in steering the submersible, but I’m told it’s quite simple.” Ms. Holiday turned her attention to Duncan. “Just remember, you are the best secret agents the world has ever seen. Isn’t that right, Alexander?”

Mr. Brand grunted but nodded.

The captain’s men helped the children into their seats. Then the vessel was raised off the deck of the Julia Child.

“Take care of my sub!” the captain called over the radio.

The Muhammad Ali swung over the side of the ship and lowered into the water. Soon, the chains that held the little submersible aloft released and it plopped into the water with a jolt. Not that the team noticed. They were already leaping to their responsibilities. Ruby took control of the onboard computer and the radar device, which was currently tracking a school of dolphins directly below them. Matilda was in charge of the mechanical arms and immediately began throwing practice haymakers and uppercuts. Jackson was getting a feel for the sub’s harpoon gun. Flinch was in charge of cameras and spotlights. He rarely blinked and wouldn’t miss anything. It was up to Duncan to steer the submersible. He sat in the captain’s chair, watching as the waves swallowed the craft.

“So that guy was once in NERDS?” Jackson said.

“Well, he’s a total hottie now,” Matilda said.

“Gross!” Ruby cried. “He’s so old.”

“I’m just saying, if he turned out that good-looking, there might be hope for us all.”

“Fishhead was on the team from 1973 to 1983,” Ruby said. “They called him Fishhead because he was a naturally great swimmer.”

“What about his upgrades?” Duncan asked.

“He didn’t have any at first,” Ruby explained. “They had a crude computer system that suggested gadgets based on a spy’s weaknesses. But mostly they were just kids who were really good at something.”

As the other kids imagined the prehistoric days of NERDS, the submersible sank farther into the deep. There was no need for Duncan to steer. Gravity was carrying the small craft to the bottom of the ocean. Duncan drifted as well, into his own thoughts: his sister’s mean comments, his parents’ confused expressions when he spoke, his anxiety over losing his upgrades. Somehow it was all tied together; he just couldn’t undo the knot. He didn’t like being confused. It made him feel like he used to before he became a spy and his whole life changed—back when he was below average.

“What’s on your mind, muchacho? And nice threads, by the way,” Flinch said as he leaned forward.

“Thanks. Just thinking about our mission,” Duncan lied.

“Isn’t this great? It’s like that book Twenty Thousand Leagues Under the Sea. You’re like Captain Nemo up here in the control seat. Whoa! Did you see that?”

Duncan looked out the window and saw a fin swim past the submersible. The only problem was, this fin was four times the size of the craft. “What was it?”

“How would I know?” Flinch said, his eyes as big as saucers. “The closest I’ve ever gotten to the ocean is a box of Swedish Fish.”

“It’s a whale,” Ruby said, following it on her radar screen. “It must weigh close to twenty tons.”

“That would make it a whale shark,” Duncan said. “It’s one of the biggest animals in the world and it’s native to this part of the ocean.”

“Whale shark?” Jackson cried as he swiveled the harpoon gun to prepare for attack.

“Relax, it’s harmless,” Duncan said.

The whale shark glided by once more, this time slowing to fix a massive eye on the craft. The children held their breath until the animal swam away, then craned their necks to follow its path. Swimming in its wake were thousands of tiny silver fish. They moved about in a single massive group, less like fish and more like a ribbon of gelatin trailing the whale shark. Suddenly, a school of tuna fish appeared from nowhere, darting in and out of the hitchhikers, feasting on the flickering ribbons of life. Duncan had never seen anything like it in the world.

“Do we not have the best jobs ever?” Flinch cried.

Just then, the front glass flickered and the image of Agent Brand appeared before them all. He looked rather irritated.

“What’s the problem, boss man?” Matilda asked. “You look angry.”

“Isn’t that how he always looks?” Jackson mumbled.

“I’m fine, Wheezer,” Brand said, though his irritated voice said otherwise.

“We haven’t found anything yet, sir,” Ruby said.

“It will take you a half an hour to make it to the spot we believe the Bom Jesus settled. I was just letting you know our sonar scans have shown that there is indeed something below you.”