Exclusive excerpt: 'The 39 Clues: Day of Doom' by David Baldacci

Here's a first look at the cover of The 39 Clues: Day of Doom by best-selling novelist David Baldacci. It's the sixth and final book in the Cahills vs. Vespers series spinoff of the popular multimedia adventure series aimed at kids 8-12. In the finale, brother and sister Dan and Amy Cahill end their worldwide scavenger hunt and must deliver a ransom to save the world. Two Cahill books have hit the top 50 of USA TODAY's Best-Selling books list. Day of Doom is in stores March 5. Read an excerpt below:

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Chapter One

The etched glass goblet sat on an exquisite marble countertop. The countertop was in the bathroom of a luxurious hotel room. The hotel room was in New York City, where luxurious hotel rooms are fairly common. The goblet looked like a reproduction antique that one might find in an eight-hundred-dollar-a-night deluxe room at the Ritz-Carlton.

Only the goblet wasn't a beautiful reproduction. The hotel hadn't placed it there. Someone else had.

And the goblet wasn't empty. It was, in fact, about to be used.

The boy reached down and gripped the goblet. In it was the potion he'd completed, a mass of reddish-green liquid that pooled in the glass container like a deadly slime about to be unleashed on the world — a description that was not so far off the mark. He lifted the goblet and touched it to his lips, and then tipped it back. The contents slipped past his lips, entered his mouth, and washed down his throat and into his belly. He gave a small shudder as the foul concoction landed firmly in his gut and his taste buds roared their disapproval.

Dan Cahill wiped off his mouth with the back of his hand, a hand that was beginning to shake. He set the goblet down on the counter. He had selected the ornately carved goblet because what he had just done was a momentous act, and he had wanted to do it in style.

He had thought long and hard before doing what he had just done. But Dan ultimately had decided that this was the only way. He walked into the living room of his suite and sat down in a plush chair, his focus completely on the empty goblet, which he could just make out through the open door. He cast his mind back to the time he had spent at Columbia University, more specifically in the science lab there. That's where, with the help of an Ekat scientist, he had manufactured this serum. Or the serum, rather. There was no other one like it in the world.

It hadn't been easy. Normally, creating the serum would require lots of time, money, and a lab beyond even what was available at Columbia. But Dan had been obsessed with producing the serum for a long time. Thus he had figured out some shortcuts in how to process it. He had always thought he might have to make the stuff while on the road. And, as it turned out, he'd been right.

He stared down at his hands. He had a reasonable idea of how long the interaction would take. Yet he was unsure of exactly what the transformation would be.

Will I turn into something like the Hulk? Big and green and possibly psycho?

A sense of panic started to leach into his brain, working its way down his spine, neuromuscular messages firing off to the rest of his body like an old-timey telegraph operator performing his dots-and-dashes SOS.

Am I in trouble? What did I just do? But what choice did I have?

Dan and his sister, Amy, had just handed their archnemesis the last elements needed to build a device that might end the world. And that outcome had taken a large psychological toll on both of them, but especially Amy. Dan and Amy had been through a lot, but Dan had never seen his sister withdraw like she had over the last twenty-four hours. He wasn't even sure that she could continue on as the leader of the Cahills. And if she couldn't, who could?

Maybe me. Maybe I'm it.

So really, what choice did I have?

The answer was painfully obvious.

None.

So he sat and waited for the serum to bring him the physical strength of a superhero and the turbocharged mental prowess of a thousand Einsteins. He could almost sense the power wave rushing at him. He stood and looked in a mirror bolted to the wall. He did this not simply because he wanted to see the transformation as it was happening. He also wanted to do this because Dan Cahill was about to disappear forever. He wanted to see himself one last time, before he became something else irreversibly.

There was also the other thing. He had no idea what the serum would really do to him. It might end up killing him. Only one person had ever taken the stuff, and that had been over five centuries ago. What Dan desperately wanted — indeed, the only reason why he had gathered the necessary ingredients and concocted the formula — was to have the serum convey on him extraordinary powers, both physically and intellectually, with which to fight and beat the Vespers. But they might come at an enormous cost. It might be that the human body was not built to contain such forces, at least not for long. But Dan didn't need to be super forever. He just needed it long enough to defeat the Vespers, rescue the hostages, and save the world.

It was a short, though substantial, bucket list.

I am willing to die for this. He mouthed the words, so he could see himself saying them in the mirror. This is the end for me. It was heady stuff for a thirteen-year-old with his whole life ahead of him.

Well, my life just got a whole lot shorter. But it's okay. It will be worth it.

He felt noble. He felt right.

He also felt nothing happening.

He stared more closely at the mirror. Same hair, same height, same bone structure. His skin was not turning green. He did not look the least bit psycho. Massive muscles were not plating themselves on top of his normal ones. He checked his watch. Twenty minutes had passed. And nothing. Something was wrong.

Something was terribly freaking wrong. Had he not done the formula correctly? Had one of his shortcuts ruined the whole process? But he'd been sooo careful.

Right then she stepped from the shadows thrown by a bulky armoire set against a far corner of the room. His sister, Amy, sixteen years old and the de facto leader of the Cahill clan, looked back at him. She was tall and pretty and unbelievably smart. And she could kick butt, too. Dan loved her. Admired her. Looked up to her. But he was also her younger brother, so it was sort of his job to make her life slightly miserable from time to time.

But Amy was a shade of her former self. Before, she had been so resilient. She had taken blow after blow and come back strong. But this time was different. Now Amy had crawled in a shell that seemed so thick and strong she might never be free of its embrace. Dan was surprised that she had even come out of her room.

"What's up, Amy?" he said casually, sliding over and trying to block her view of the goblet through the opening into the bathroom. "You feeling better?"

"I'm sorry," she said.

"Sorry about what?"

"For acting like a wuss. For crawling inside myself because it seemed like the Vespers had won. But I'm back now, Dan. I'm ready to take up the fight. I won't let you and the others down like that again. This is a fight we all have to finish, and we're going to do it together."

Dan couldn't keep from smiling. This was the Amy he had been waiting for. No matter how tough things got, she always came back. But then he felt immediate guilt and more than a little panic. He'd already taken the serum.

As though reading his mind, she quickly moved to the side and glanced at the goblet through the bathroom doorway and then at her brother. Her look was a guilty one, yet her lips were set in a firm line. Dan sensed that she was about to make his life miserable.

She said in a halting voice, "I couldn't let you do it, Dan. I just couldn't."

It took a long moment for Dan to process her words. When he finally did, he blurted out, "What did you do?"