"Open to you commands, Master your, Nomis." Jenna forced the words from her mouth. She had never uttered a Reverse Incantation before and hoped she never would have to again, but now she had no choice. The Wurm Burrow was sealed with a massive plug of immovable iron, and Jenna knew that if she turned that into chocolate there was no way she would be free by morning. She held her breath, hoping that she had remembered the Incantation correctly.

She had. To her relief, the thick iron plug swung silently outward, and the dim moonlight of an old moon filtered into the Wurm Burrow, along with a gust of wind and a few drops of rain.

"Come on, Thunder, come on, boy," whispered Jenna, encouraging the reluctant horse out into the night with a chocolate pebble. The dark quarry was not a pleasant prospect; a mournful wind was howling and sweeping down the ravine, bringing with it the beginnings of a cold rain. Jenna pulled Lucy's cloak around her, shivering as the chill night air hit them. Then she led Thunder down the steep path from the Burrow onto the track that ran along the side of the ravine.

"Hold still, hold still, Thunder," she whispered, as the horse looked about nervously and flicked his ears, listening to the night sounds. Jenna swung herself up into the saddle, wondering how Thunder would take to a new rider. The horse did not object,maybe because he had already become used to Jenna during the long day's ride. When Jenna said, "Walk on, Thunder, walk on," and gently pressed her heels against the horse's flanks, Thunder moved off at a leisurely pace, heading back down the track that he had struggled up only a few hours before.

Jenna felt quite at ease with the huge horse. Although he belonged to Simon, Thunder seemed a good-natured animal, and he walked surefooted along the track while Jenna sat bolt upright, scanning the sheer rock face for any signs of movement. The sooner they were through the ravine, she thoughtencouraging Thunder into a brisk trotthe better.

As they rounded the first bend, Thunder came to a sudden nalt. A landslide blocked their path. "Oh, no," gasped Jenna.

There was no way through. A huge pile of jagged boulders and massive slabs of slate had fallen across their path. To their right was a sheer rock face and to their left, at the bottom of the ravine, was the riverflowing fast and dangerous.

They would have to go back.

Jenna tried to coax Thunder to turn around but the horse refused to move. He shook his head and his bridle jingled noisily.

"Shh, Thunder," soothed Jenna. "Come on, around you go." But Thunder would not budge. Heart in her mouth, Jenna slipped off the horse and led him round with the help of another chocolate pebble. Then she was straight back in the saddle again and, with a heavy heart, retracing their steps back up the track, back toward the Burrow.

It was tough going. Thunder was now walking into the teeth of the wind, but he was happy that he was heading for home. When they reached the small path that led to the Burrow, Thunder stopped, expecting Jenna to get off and lead him back to his warm stable.

"No, Thunder, you're not going home. Walk on." Thunder shook his head, jingling his bridle again.

"Shh. Please, Thunder. Walk on," Jenna whispered as loudly as she dared, terrified that somehow Simon would hear her. She gave the horse a determined kick and Thunder very reluctantly moved off. Jenna glanced behind them, half expecting to see Simon emerge from the Burrow, but the iron plug still gaped open and showed nothing but a dark, empty space.

After they had passed the Burrow the track leveled out, which made the going easier for Thunder, but the wind began to strengthen and, with it, the rain became heavier. Dark clouds blew in and a sheet of lightning silently lit the jagged tops of the ravine. A few moments later the rumble of thunder reached them.

Jenna and Thunder pressed on. The moonlight dimmed and the quarry became dark, lit only by the lightning playing across the sky. The wind howled down the ravine, blowing stinging rain into their faces. Both Jenna and Thunder half closed their eyes and kept their gaze fixed firmly on the trackuntil a movement high in the rocks ahead caught Jenna's eye. She looked up, hoping that it was just a scudding cloud that had caught her attention. But it was something much more substantial than a cloud.

It was the blunt gray head of a Land Wurm.

A Land Wurm takes a long time to come out of its Burrow, and Jenna had caught sight of the Wurm as it first poked its head into the night air. She knew, from travelers' tales that Silas used to tell, that it was not the Wurm's head that was the dangerous part; it was its tail. The tail of a Land Wurm was fast and deadly; when a Land Wurm had you in its sights it would flick its tail like a lasso and drop it over your head. Then it would coil the tail around and crush you. Very, very slowly. Although sometimes, Silas had told her, if the Land Wurm was not particularly hungry, it would carry you back into the Wurm Chamber and store you for a while, still alive, in order to keep you fresh. A Land Wurm preferred fresh meat, still warm.

Jenna remembered an occasional visitor to the Heap rooms who, among the younger Heaps, was known as Dribbly Dan. Dribbly Dan had a wild look in his eyes and had scared the younger ones, but Silas had told them to be nice to him. Dan had, according to Silas, been a completely dribble-free quarry worker until he was taken by a Land Wurm and kept in the Wurm Chamber for three weeks. He had survived by licking Wurm slime and eating rats. He had finally managed to escape one night when the Wurm had been tempted out by a large flock of sheepand an inexperienced shepherdthat had wandered into the quarry. But Dan had never been the same after his three weeks in the Wurm Chamber.

There was no way that Jenna wanted to end up like Dribbly Danor worse. She looked up at the Wurm, trying to judge whether to speed up and go past it or whether to stop and turn back yet again. But Jenna knew that if she turned back she would be caught between the Land Wurm and the landslide, and between them would be Simon's Burrow with Simon quite probably awake by now and searching for her. She had no choiceshe had to get past the Wurm before its tail was free of the Burrow.

"Gee up, Thunder," Jenna said in a low, urgent voice, giving the horse a nudge with her heels, but Thunder just kept up his slow trudge through the wind and the rain. Jenna glanced at the Wurm again. Its Burrow was high above them, and still quite distant, almost at the top of the old quarry workings that rose from the track. The Wurm's head was now well out of the Burrow, and Jenna saw that its dim red eyes had locked onto her and Thunder.

"Get on, Thunder," Jenna yelled in the horse's ear, giving him a hard kick at the same time. "Or do you want to be eaten by a Land Wurm?" She flicked Thunder with the reins, and suddenly Thunder put his ears back and took off like a rocket, galloping along the track as if to show Jenna that if she wanted fast, then fast was exactly what she was going to get.

As they galloped toward the Land Wurm, Jenna could tell that the creature had seen them coming; it was pouring out of its Burrow at full speed, like a thick, never-ending stream of gray sludge.

"Go, Thunder, go!" Jenna screamed urgently above the howl of the wind and the rain as the horse pounded along the track, taking them ever closer to the Wurm. Still the Wurm came streaming out, slipping down the rock face so fast that Jenna suddenly realized she could not be sure that Thunder would get past the Wurm before it reached the track. She crouched down on the horse like a jockey, keeping the wind resistance low and talking in his ear, encouraging him on. "Go, Thunder, go, boy ... go/"

And Thunder went, galloping at full tilt now, as if he too knew that both their lives depended on him. As the Wurm reached the bottom of the cliff, and Thunder was closing the gap, Jenna looked up to see if the tail was free of the Burrow. There was no sign of it yet, but she knew that any moment it could come shooting out. She turned her attention to the path just in time to see the Wurm's head reach the track.

"Go, Thunder," she yelled, and then, as the Wurm slipped across the track and barred their way, Jenna screamed, "Jump, Thunder!"

Thunder jumped. The powerful horse sailed into the air and took them high above the great gray monstrosity that slithered below them. And as Thunder landed on the other side of the Wurm and galloped onward, the Wurm's tail whipped out of the Burrow and shot through the air with a crack.

Jenna felt the wind whistle and heard a bang as the tip of the tail sliced the top off the rock behind them. She could not stop herself from looking backthe tail had missed them by no more than a few feet.

The weak red eyes of the Land Wurm followed its prey along the track and the tail gathered for another strike, whirling itself high into the air like a huge lasso. But, as it smashed down onto the track for the second time, Thunder cantered around a tall rocky outcrop, and the Wurm lost sight of them.

Thump! Something landed behind Jenna.

Jenna wheeled around in the saddle, ready to fight the tail with all the strength she possessedbut there was nothing there. All she could see was the steep slate outcrop rapidly disappearing into the night as Thunder galloped on.

"Phew," said a small, slightly querulous voice behind her. "You cut that ... a bit fine. Nearly gave me ... a heart attack ... that did."

"Wh-who's that?" asked Jenna, almost more scared of the strange little voice than she had been of the Land Wurm.

"It's meStanley. Don't you remember me?" The voice sounded somewhat aggrieved. Jenna peered into the darkness againthere was something there. It was a rat. A small brown rat lay sprawled across the horse's back, desperately clinging to the saddle.

"Could you just ... stop for a mo while I ... sort myself out?" the rat asked, bouncing around on Thunder's back as the horse galloped into the night. "I think I've ... landed on my sandwiches."

Jenna stared at the rat.

"Just slow ... down ... a bit," he pleaded.

"Whoa, Thunder," said Jenna, reining the horse in. "Slow down, boy." Thunder slowed to a trot.

"Ta. That's better." Still clinging tightly to the saddle, the rat hauled himself to a sitting position. "I'm not a natural horse rat," he said, "though I suppose they're better than donkeys. Don't like donkeys. Or their owners. Mad as snakes the lot of them. Don't get me wrongI don't mean that about horses. Or their owners. Perfectly sane. Most of 'em at any rate, although I must say I have known some that"

Suddenly Jenna remembered who the rat was. "Message Rat!" she gasped. "You're the Message Rat. The one we rescued from Mad Jack and his donkey."

"Got it in one," grinned the rat. "Spot on. But yours truly is no longer a Message Rathad a bit of an argy-bargy with the Rat Office in the bad old days. Ended up in a cage under the floor for weeks. Not nice. Not fun. Got rescued and retrained with the"the rat stopped and looked around as if to check whether anyone else might be listening"Secret Rat Service," he whispered.

"The what?" asked Jenna.

The rat tapped the side of his nose knowingly. "Very hush-hushknow what I mean? Least said, soonest mended and all that."

"Oh," said Jenna, who did not have the faintest idea what the rat meant but did not want to get into a conversation about it just then. "Yes, of course."

"Best thing I ever did," said the rat. "Just finished my training last week in fact. And then, blow me down, my first mission is tor the ExtraOrdinary. Quite a coup, I can tell you. It impressed the lads on the course."

"Oh, that's nice," said Jenna. "So what's this mission, then?"

"Find and return. Priority number one."

"Ah. So who do you have to find and return?"

"You," said Stanley with a grin.