He could feel something happening in his helmet and assumed Benjamin was tinkering remotely.

And then there was another commotion in his ears. It sounded like someone had tossed a chair across the room. “What’s going on?”

“It’s another member of the science team,” Mr. Brand said. “He’s showing symptoms. We’re dealing with it. Just focus on your mission. If you destroy the transmitter soon, they won’t be sick much longer.”

“OK. Let’s go then.”

But he would have to wait. From the corner of his eye he saw more beanbags, but these were white and they were coming right for him. “Um, I think the white blood cells have found me.”

He took a long drink of fruit punch and went on the offensive, socking the first one with a huge punch. It exploded all over him. “Gross!”

Two more came from behind. He leaped up and delivered a roundhouse kick that exploded them as well. But that wasn’t the end of the assault. A hundred more white blood cells were swirling up the artery, preparing to kill him.

“Flinch, report!” Brand cried.

“I’m a little busy,” he said, drinking more juice. Full of sugar, he punched and kicked and slammed with all his might. One cell fell after another, but there were too many—more than any one person could handle, no matter how strong and fast.

“Can I use the laser?!” Flinch asked.

“Carefully!” Dr. Kim replied.

Flinch turned on the weapon, aimed it, and fired, cutting the cells in half as they approached. One after another they fell, but each one was replaced by ten more. Soon they had him backed up against the wall of the artery with nowhere else to go.

“I have to get out of here,” he said, turning the laser on the wall of the lung. He cut a hole big enough for him to squeeze through, then fought his way toward the opening. The cells were everywhere. One latched on to his arms, then his legs. Others clung to his juice pack. He kicked at them, but they stuck like glue, and worse, they were trying to puncture his suit. With a huge twist on his harness, he felt a wave of sugar so intense he could do nothing but shake. He was so out of control, he couldn’t speak, but it worked. The supershaking dislodged the cells. The moment he was free, he readjusted his harness then dove into the hole.

Unfortunately for Flinch, the inside of the lung was even more treacherous. He was battered and squeezed as it expanded and contracted. The feeling reminded him of a camping trip he had gone on with his parents shortly before they passed away. They had all devoured a dozen sacks of roasted marshmallows, then crawled into their brand-new sleeping bags. That’s when the good times turned into a sugar-fueled nervous breakdown. His sleeping bag was so tight and constraining, Flinch felt wrapped up in the body of an anaconda. In the middle of the night, he crawled out of the tent and threw the sleeping bag in the river. Heathcliff’s lungs felt like that sleeping bag.

“I’m in the lungs,” Flinch said, fighting back panic. “Get me out of the lungs!”

“Just keep moving forward. You need to find another artery. This one will be large. It’s called the aorta, and it will take you directly to the base of the brain,” Benjamin chirped.

Flinch crawled forward, unable to see more than a few feet in front of him. The noise and the wind of the lungs were so intense. It felt as if he were inside a hurricane. Benjamin turned the volume on the suit all the way down, but the sound still raged in his ears. He tried to breathe steadily so that he wouldn’t hyperventilate. The last thing he needed was to pass out inside of Heathcliff. He pressed on and finally found another of the massive tubes.

“Just a small slit,” Dr. Kim said. “The aorta is a major artery. If you cut too big it could kill Heathcliff in minutes.”

Flinch did as he was told and gingerly sliced a hole just big enough to squeeze through. This time he was ready for the fast-churning bloodstream and managed to not lose total control of himself.

“This will only take a few seconds,” Dr. Kim told him. “And then you’ll be at the base of the brain. The transmitter is buried inside the left hemisphere of Heathcliff’s brain. When you see an enormous gray mass, fire your tether into the wall of the artery.”

Flinch couldn’t miss the gray mass. It was huge and right above him. He fired the tether and lodged himself in place. He eyed Heathcliff’s amazing brain. Flinch could almost see the evil ideas it was conjuring.

“It’s a wonder,” Dr. Kim said.

“It’s gross,” Flinch said.

Dr. Kim laughed. “Unlike the twisted mess that is Heathcliff’s body, his brain is very much unchanged—except for its size. All of the regions seem to be like any other human brain. I’m pulling up a map right now to help guide you.”

But Flinch stopped listening to the scientist midway through her explanation. Hanging over his head, high in the cavernous reaches of Heathcliff’s skull, were thousands of black, shiny creatures. They were clinging, heads down, to the boy’s brain, like sleeping bats with eyes that glowed neon green. Every one of their eyes was turned to Flinch.

“Uh-oh,” Flinch said.

Two of the creatures flew down and buzzed by his head as if they were just interested in getting a better look. Then they zipped back up to join the others. The creatures chattered back and forth and then, all at once, like a crowd that has just witnessed the hometown team lose in the final second, all of their voices roared with anger.

“Uh-oh,” Flinch said again.

“What’s ‘Uh-oh’?” Brand asked.

“The nanobytes know I’m here,” Flinch said as the creatures scurried out of the gray meat and ran toward him, clicking their legs together like beetles. Flinch took a few more greedy gulps of juice, and, with sugar racing through his bloodstream, he could only think of one thing to do: run right at them with fists clenched. He stomped through them like a rampaging rhino, snatching two by their necks and smashing them together, causing them to explode into a thousand pieces of metal and circuitry. He punched another one’s head off its shoulders, then snatched one of its spindly limbs to use as a club on a dozen more.

“C’mon, ugly, let’s dance!” he shouted at one, which was soon a pile of broken robot parts. More and more came. He drank his juice and pounded his chest and shouted, “I AM MIGHTY!”

WELL, SO FAR YOU’VE DONE PRETTY WELL, OR MAYBE I JUST HAVEN’T BEEN CHALLENGING YOU. SO I’M GOING TO THROW OUT THREE VERY INTENSE TASKS. IF YOU CAN ACCOMPLISH THEM, THEN I WILL TIP MY HAT TO YOU AND HAPPILY REPORT THAT YOU ARE IN TIP-TOP SECRET AGENT SHAPE. THINK YOU’RE UP FOR THIS? GOOD!

CHALLENGE #1: ARM-WRESTLE A TRUCK DRIVER

YOU ARE A BRAVE SOUL. TRUCK DRIVERS ARE NOTORIOUSLY SURLY CHARACTERS WHO ENJOY A GOOD BOWL OF CHILI, THE OPEN ROAD, AND TEARING AN OPPONENT’S ARM OFF IN A GAME OF STRENGTH.

FIRST, FIND A TRUCK DRIVER. SECOND, FIND A DINER WITH A LOOSE POLICY ABOUT THIS MOST VENERABLE GAME. THIRD, SAY SOMETHING MEAN ABOUT THE TRUCK DRIVER’S MOTHER.

FORGET WHETHER OR NOT YOU WON—IF YOU SURVIVED, THEN YOU’RE A WINNER IN MY BOOK.

CHALLENGE #2: WRESTLE A BEAR

DON’T GIVE A THOUGHT TO THE FACT THAT THIS SKILL IS TOTALLY IMPRACTICAL, SINCE THERE ARE ONLY, LIKE, THREE BEARS WORKING AS ENEMY SPIES, SO THE ODDS OF BEING ON A MISSION WHERE YOU ENCOUNTER ONE SPYING ON YOUR COUNTRY IS PRETTY LIMITED.

FIRST, FIND A BEAR. SECOND, GET REALLY CLOSE TO THE BEAR AND POKE IT WITH A STICK. THIRD, THE REST WILL TAKE CARE OF ITSELF.

CHALLENGE #3: WIN THE OLYMPICS