he mouses take a nap?" said Boots. "Kill the lights!" Gregor shouted at the fireflies. In another few seconds even Boots would realize that the mice were not sleeping but dead. Some lay in pools of dried blood. The eyes of others were wide open as they stared frozen into space. "Turn them off!"

The bulbs on Photos Glow-Glow's and Zap's rear ends went dark. Gregor flicked on the flashlight at his belt but did not direct it to the ground.

"What did Boots say? What mice? Did we find the nibblers?" asked Hazard, struggling to sit up.

"Lie back, Hazard; there is nothing to see," said Howard.

"What is that smell?" Hazard insisted.

"It comes from a foul stream. We will fly on," said Luxa.

None of them wanted Hazard or Boots to see the corpses. But there was no concealing them from Thalia. When they found a place to land about a thousand yards beyond the graveyard, Gregor noticed the little bat was trembling. He felt pretty shaky himself.

Howard made a bed for Hazard and then pulled Luxa and Gregor aside. "One of us must stay with the young ones while the other two go back."

"I must go," said Luxa.

"You stay, Howard. In case Hazard feels bad or something," said Gregor.

They left Howard, Nike, and Temp to watch over Hazard, Boots, and Thalia. Photos Glow-Glow stayed at the campsite while Zap escorted Gregor and Luxa and their bonds back to the mice.

Before they left, Howard provided them with cloths wetted with an antiseptic solution to hold over their noses as a barrier to the smell of decomposing flesh. "Do not touch any of them," he instructed. "You do not know what contagion they might carry."

The cloths helped, but when they reached the mice Gregor still could not help gagging at the stench. Zap's light was enough to illuminate the whole area. The bottom of the tunnel had ended with a sheer drop of about forty feet. The mice must have been driven straight off the side of the cliff and fallen to their deaths. Some, by their squashed and battered appearance, had clearly broken the fall of others. Several pups were crushed completely. There were no rats among the dead.

Even Zap, who showed remarkably little compassion in general, seemed affected by the scene. "What a waste. What a waste. I do not pretend to like the nibblers, but what a waste."

"I guess they ran right off the edge of the cliff," said Gregor.

"They would have found a way to scale the wall, had they been given time," replied Luxa bitterly. "This was the gnawers' work."

"Should we do something with the bodies?' asked Gregor.

"There is nothing to be done. If we place them in the water, we pollute our own drinking supply. We do not have enough hands to bury them in stone, nor the fuel to burn them properly," said Luxa. All this was true. Yet somehow they couldn't just fly away and do nothing.

"We should leave something, a headstone or some message," said Gregor. But writing in stone was no small matter. He had intended to write a few sentences about what happened, but it was an effort even to scratch one straight line into the side of the cliff with his sword. As he stood considering the wall, waiting for inspiration, Luxa came up and added the thin, beaklike appendage that turned the line into the scythe. Into a mark of secret.

"It will be a warning to any that follow us," she said. "And it will be a fitting marker for the nibblers' graves."

And then Luxa did something that made Gregor feel both remarkably close to and a million miles away from her. Flinging away the cloth from her nose, she kneeled on the ground and placed her crown in front of her. Crossing her wrists, she held her hands, palms down, over the gold circle, and said in a loud voice:

"Upon this crown my pledge I give.

TO MY LAST BREATH, I HOLD THIS CHOICE.

i will your unjust deaths avenge, All here who died without a voice."

The words reverberated around the tunnel. It was not an impromptu rhyme, something she had made up off the top of her head. There was a specific ritual and a grim, formal tone to the lines. Gregor was certain it was an oath. Something you swore to fulfill or died trying to. It came from such an agonized place within Luxa that Gregor wanted to wrap his arms around her. But the oath had pushed him away from her, too. Had reminded him that he was just a visitor in a strange land where people vowed vengeance and crowns mattered and queens were off-limits to him.

Watching her rise, Gregor could no longer see Luxa the twelve-year-old girl who'd been searching for clues about her mouse friends. What he saw was the future head of Regalia, and its considerable armies, and that the rats were somehow going to pay with their blood.

Something was happening in the tunnel. Faint whispering sounds, buzzes, a rustle of wings. Gregor remembered what Howard had said, about how a lot of creatures lived in Hades Hall. They had been keeping a low profile so far, but they were around, watching, listening, and now reacting to Luxa's little speech. She heard the reaction and for some reason that Gregor didn't understand, she smiled.

The moan startled them. Zap brightened her beam and they saw a slight movement in the field of stillness. The tip of a tail shuddered. Disregarding Howard's warning about touching the creatures, Luxa raced to the mouse's side and crouched beside him, stroking his fur. He could not speak.

"Let's get him to Howard," said Gregor. Together, he and Luxa loaded the mouse onto Ares's back. Gregor tossed his leg over his bat's neck, but Luxa remained on the ground. "Aren't you coming?" he asked.

"No, Gregor. We will stay and make sure no others still have light," said Luxa. In the Underland, the word "light" could be interchangeable with the word "life."

Gregor looked at the victims. "We'll come back and help," he said.

"You do not have to," said Luxa. "Aurora and I can manage."

"We will come back," Ares said.

Gregor and Ares delivered the barely conscious mouse to Howard and returned to the base of the cliff. One by one, they checked each body. Some were obviously dead. Some it was impossible to tell, so they felt for a pulse or listened for a whiff of breath coming from their nostrils. There were no other survivors.

Back at the campsite, Gregor scrubbed himself at a nearby stream, but he could not seem to get the smell of the dead mice from his pores. And the images of those bodies... well, he knew those would revisit him for a long time in his dreams.

Howard worked long and hard over the injured mouse. One of his front legs was broken, so Howard set the fracture. He put a salve on the mouse's raw and bloody paws. After about an hour of periodically getting him to take spoonfuls of water, Howard made a thin gruel of fish, bread crumbs, and broth and got the mouse to eat a little. The water and food revived him enough for him to speak a few words, starting with his name, Cartesian. Howard was able to ascertain the extent of Cartesian's injuries better now. The mouse had badly bruised ribs, although they did not seem broken. He'd received a blow to the head. Dehydration and hunger had also taken their toll. It was not enough information to find out exactly what had happened to Cartesian, but it was enough to treat him. Howard made a poultice for Cartesian's head, gave him some painkiller and a second medicine to reduce swelling, and continued to feed him.

Boots wanted very badly to help, so Howard gave her the job of singing the mouse to sleep. She squatted down a few feet away and softly sang little tunes she knew from home. These were mostly theme songs from preschool shows she watched on TV. Then she launched into her Underland repertoire, which included the songs about the spinners, and the fish, and the bats.

"Bat, bat,

Come under my hat, i will give you a slice of bacon

And when I bake, I will give you a cake,

If I am not mistaken. "

Then she sang the stanza from the one about the queen and the nibblers and pouring tea, because she thought, as a mouse, Cartesian would like it best.

"Catch the nibblers in a trap. Watch the nibblers spin and snap.

Quiet while they take a nap.

Father, mother, sister, brother,

Off they go. I do not know

If we will see another. "

Cartesian slowly drifted off to sleep, and Howard praised Boots for her excellent singing job. Enamored with her newfound talent, Boots went around to everybody trying to sing them to sleep. Half the party were so tired they genuinely fell asleep; the other half pretended until Boots dozed off herself. Then Gregor, Luxa, Howard, Aurora, Nike, and Ares gathered for a consultation in the glow of Photos Glow-Glow's bulb.

"Well, as tragic as our findings today have been, at least we know we have kept to the nibblers' trail," said Howard.

"It is not much to our credit," said Luxa. "We chose this path because it was the only way out. We can be sure that we follow them to the far side of Hades Hall."

"And then?" asked Gregor.

"And then what?" asked Luxa.

"And then you're going to keep following them, aren't you? Instead of going back to Regalia," said Gregor. She didn't answer, but he knew he was right. She wasn't going home. Not after she'd kneeled on the ground and said that stuff over the crown.

"We cannot do that. We have injured who must be returned home," said Howard. "And I believe there is enough evidence to make a case before the council, now that we have Cartesian for a witness."

"The rest of you will go back. Aurora and I will continue after the nibblers," said Luxa. "Someone must stay on their trail."

"But it will not be you, Cousin. I will drag you back to Regalia before I would leave you here alone," said Howard.

"She made some kind of oath," said Gregor. "Back at the cliff."

"Oath?" Howard looked at Luxa and his face fell. "Not 'The Vow to the Dead'?" he said in a hushed voice. Luxa nodded. "Oh, Luxa, what have you done? You are not even of age. You do not reign. The army does not move at your command. How mean you to fulfill it?"

"The only way I can," said Luxa. "I will go after the nibblers, and the council will send the army after me."

"They didn't send an army when you got caught in that rat maze," said Gregor.

"Because they thought she was dead," said Howard. "They will now. They must. Especially if she has said the vow."

"How will they even know?" said Gregor. "It's not like the humans have scouts in Hades Hall."

"Do you think only human ears matter?" scoffed Photos Glow-Glow. "The fliers heard her; that nibbler heard her; Zap heard her and has already told me. You are in Hades Hall, not the Dead Land. Who knows how many other creatures sat in the dark listening?"

"A lot," thought Gregor, remembering the strange noises that had followed Luxa's vow. That's why she had smiled. She had wanted them to hear.

"Half the Underland will know she said it in a matter of hours; she cannot take it back," said Howard.

"Nor would I if I could," said Luxa.

"But you're only, like, twelve," said Gregor. "Does it even count?"

"In this case, it counts," said Howard. "By the time word of the vow reaches the council it will already have reached our enemies. There will be no way to call it back or deny it. And given the circumstances, we will have only one option."

"What's that?" said Gregor.

Luxa gazed at him evenly. "I have just declared war on the rats."