regor squinted into the ashy gray light and finally made out the nibblers. They were walking single file down a long curved path that began at what looked like the mouth of a tunnel high in the rocks and that led to a pit at the base of the volcano. On one side the path ran along the edge of a sheer cliff with sharp rocks at the base. A stone wall ran along the other side of the path, blocking the view of the pit from their sight. It wasn't until the nibblers were almost at the bottom that they realized where the rats were sending them.

The nibblers who had reached the pit began to squeal out warnings to those following them. Gregor could see the alarm spreading up the path. Mice turned and tried to force their way back up, some literally crawling over the backs of the others to try to reach the tunnel at the top. A handful made it only to be driven back by rats. Then the mice began to shriek as a large boulder was rolled into place, sealing the mouth of the tunnel. They threw themselves against the boulder but could not budge it.

"Let us go!" cried Luxa, jumping to her feet.

"And do what?" asked Ripred, stepping in front of her. "You, all of you, you've got to stop running into dangerous situations without using your heads! There is no faster way to get killed!"

"We can carry them out of the pit to safety!" said Luxa.

"Yes, a handful of them. But there are hundreds trapped down there. Do you not think the rats might notice an airlift going on? And then what? We lose the one element we have in our favor. Surprise," said Ripred.

"Then what do you want us to do?" demanded Luxa. "Wait for the volcano to smother them in lava?"

"I want you to think about it a moment!" snapped Ripred.

"Vis for volcano," Boots reminded everyone. "And valentine." She poked Ripred on the haunch with her scepter. "Valentine!" Ripred sighed. "Why are you here?"

A gust of wind swept by, drawing everyone's attention. "Oh, great. The currents are starting up again," thought Gregor. If they became too strong, the bats wouldn't be able to navigate them. At least they were clearing the air a little. One overriding current seemed to be blowing out of a nearby cave. It was sweeping the ashy haze toward the nibblers and giving Gregor his first breath of clean air in hours.

"Look, the nibblers are taking action," said Howard.

The mice had overcome their initial panic and were organizing themselves to carry out an escape plan. They had begun to build a pyramid by bracing themselves along the far wall of the pit. A single row of mice formed the base. Others were swarming onto their backs swiftly. The pyramid was rising before their eyes.

"That's smart. A pyramid," said Gregor.

"No, it is the Isosceles Maneuver," said Cartesian.

Gregor looked at him. For the first time since Cartesian had joined them, the mouse seemed lucid. "What's that?" Gregor said.

"It is not a true pyramid, for it has three, not four, points. Rather, they aspire to mimic a two-dimensional triangle," said Cartesian.

"Oh," said Gregor. It seemed to him that at home almost anything with people standing on top of other people was called a pyramid, but he didn't feel like arguing the point with Cartesian, especially after all the mouse had been through.

"See, they have a plan. Let's work with it," said Ripred. "What they need is someone to hold that path if the rats come through."

"Then we will do so," said Luxa.

"Agreed. Temp, watch the pups. The rest of you mount up," said Ripred.

Gregor was about to jump onto Ares when Ripred stopped him. "No, I'll need him to get to the path. Ride with someone else and change over when he drops me off."

"Here, Gregor," said Howard. He extended a hand and pulled Gregor up behind him on Nike.

"We should wait until the boulder begins to move. That will give us time to reach the path but not alert the rats to our presence beforehand," said Luxa.

"Good. Very good. Now you are thinking," said Ripred. "Everyone wait for it, as she says."

They sat watching, tense and poised for takeoff.

The mouse pyramid was nearing the top of the pit. Soon they would be able to begin freeing themselves. Still the boulder didn't budge.

"If there were to be lava, would we have some warning?" asked Howard.

"Generally, I believe there's a rumbling, some sort of sound," said Ripred. "Although I am no expert."

The first nibblers began to climb over the edge of the pit. The escape plan was working.

"Maybe the rats won't come back," said Gregor. "Maybe they didn't figure the mice could get out."

The mice were sending the pups up now. Trying to save them first. When five little ones had reached the top, a pair of full-grown mice began to corral them away from the pit as fast as possible. No rats appeared to interfere.

Back in the tunnel, they watched silently for a few more minutes.

Then Luxa broke the silence. "Something is wrong. Why would the rats allow this?"

"They wouldn't," said Ripred. He paused. "Unless they were expecting something else to do their work for them."

"But there's no lava. The volcano isn't even erupting," said Gregor. Suddenly Temp began to wave his antennas, his feet stepping nervously on the ground. "Not lava, it be, not lava," said the cockroach.

"What is it, Temp? What's wrong?" asked Gregor. One thing he had learned from past experience: If Temp was alarmed, there was good reason.

"Not lava, it be... it be —" Temp did not know the words for it. He broke off and began clicking in agitation.

"What's he saying, Hazard?" asked Gregor.

"I don't know. It doesn't make sense. I think he's saying the volcano is breathing," said Hazard.

Boots puffed out her cheeks and blew a stream of air in Gregor's face. "Like this. It goes breathing like this." She blew again. "Like balloon goes out."

"The nibblers. Something is happening to them!" said Howard.

Gregor squinted to make out the scene in the distance. His eyes flew to the boulder first to see if the rats had pushed it aside, but it was still fixed in place. He scanned the mice. They looked okay. They looked fine. Then one mouse at the top of the pyramid fell. Then another. Then the entire pyramid disintegrated.

Every last mouse left in the pit had collapsed in a heap. But they weren't dead. He could see their bodies flailing around.

Chaos broke out in the cave.

"What is going on?" cried Gregor.

"We must go!" cried Luxa.

"Not go, you do, not go!" begged Temp.

"Take flight, Aurora!" insisted Luxa.

Aurora seemed as eager to go as her bond. She extended her wings to take off. With lightning-fast speed Ripred leaped at the pair, flipped Aurora onto her back, and threw himself across her body. Luxa, who was trapped under Aurora's shoulder, yelled at him furiously, but Ripred completely ignored her.

Gregor upended his backpack, dumping the contents on the ground, and snatched the binoculars. He trained them on the mice and felt his heart start to pound.

"What do you see, boy? What's happening to them?" said Ripred.

Gregor stammered as he tried to describe the nightmare unfolding before his eyes. "I don't know! They can't! They —" The mice were rolling on the ground, pawing at the air, at their necks, their bodies wracked with terrible spasms. "They can't breathe!" he finally burst out. "They're suffocating!" Luxa was screaming like a maniac. Hazard pushed on Ripred's shoulder, trying to move him. "Let her up! Let her up!"

Howard grabbed Hazard and forced the boy's face into his shoulder. "No, Hazard. She cannot go. She cannot help them," he said. Tears streamed down his cheeks.

Now they could hear the desperate screams coming from the pit. Cartesian limped to the cave opening and tried to fling himself into the air, to either catch a current to help the other nibblers or simply kill himself. Gregor didn't know which. But Ares caught Cartesian before he fell.

"It's poisonous gas," said Ripred. "It must be leaking from the volcano."

"But I can't see it! I can't see anything!" said Gregor. His hands shook as he tried to adjust the binoculars.

"It has no color," said Howard.

"Nor odor that I can detect," said Ripred, his nose twitching furiously. "Of course, the wind carries it away from us — will you hold still!" he growled at Luxa. "Temp, are we in any jeopardy here?"

"Heavy, the poison be, heavy," said Temp.

"Then it's all settling in the pit," said Ripred grimly. When Gregor saw a pup, gasping to draw air, fall lifeless from its mother's back, he had to drop the binoculars. But now that the currents had cleared the air, the nibblers' agony was visible from the tunnel. They went into convulsions, teeth snapping on empty air, claws lashing out to battle an enemy they couldn't see.

"Nike, can you shield Thalia's view?" said Howard. "She has seen too much!" Nike enveloped Thalia in her wings.

"Come here, Boots!" said Gregor, scooping up his sister and laying his hand over her eyes to block the gruesome scene, although it did not seem to be upsetting her. She wriggled to get free.

"No, Gre-go, I want down!" said Boots.

"Get off of me!" Luxa freed her sword and stabbed it into Ripred's shoulder.

"Aah!" cried the rat, leaping back. Blood poured from the wound. His gums pulled back, showing his newly sharpened teeth.

Aurora righted herself and Luxa sprang to her feet, Ripred's blood dripping off her blade.

Gregor dropped Boots and was pulling his sword to step between them when Ripred snarled at Luxa,

"Fine, you stupid brat! Fly right into it and get yourself killed!"

"Shh," said Boots, putting her forefinger to her lips. "You are too loud."

Luxa spun around to the cave mouth, preparing to mount Aurora. Then Luxa saw the mice and froze, one hand clutching the fur at her bat's neck.

The screams had faded away. Here and there was a bit of movement. Then all was still.

The only sound in the cave was Howard, softly weeping.

"Shh," said Boots, patting him. "Shh. The mouses are sleeping."