"Charcoal," Rosethorn and Frostpine announced at the same time.

Niko added, "Sulphur."

"Nitre," Gorse told them, and Rosethorn nodded.

I couldn't have done it so fast, Daja remarked silently to the other children. They nodded, agreeing.

The adults argued for half an hour over the proportions of each substance. At last they managed to agree: ten parts sulphur, fifteen parts charcoal, and seventy-five parts nitre.

"It's so basic!" Lark said then. "So - so simple! And it won't take much to make it explode, once you get through the protections on the containers."

"Which is why the containers have been so well protected magically," added Frostpine.

"But what makes it boom?" Daja asked, worried. "What if it-"

A crash split the air outside, making everyone flinch. Seconds later, they heard another loud bang, from the eastern side of the temple.

"They've started again," whispered Daja. Tris was trembling.

"Let's go outside," Niko said, brushing the spoonful into the bag. "We can try to make it boom there. Fire does the trick, if what Tris and I saw on Bit was right."

In front of Discipline, on a bare spot in the path, Niko dumped a pinch of the black powder on the ground. Someone brought a long, burning reed, and Niko touched the powder with it from a couple of feet away. As a boom-stone exploded over the south half of the temple, a tiny heat of powder flared and was consumed.

"They have to leave a gap in the spells on the containers."

Rosethorn pointed out, "so their mages can light the stones in the air."

"Will our battle-mages find the gaps in time to explode the stones before they reach too close to us?" Frostpine wanted to know.

Niko poured more powder, half a cupful, on to the path, then wiped his forehead with one hand, leaving a dark stream. "Everybody stand back when I light this." He held the reed out to Gorse, who touched it with a finger. Flame leaped and bloomed on the tip of the reed.

"But the little sample just burned," Lark said. "How do they make it boom?"

"Perhaps you need more?" suggested Rosethorn as everyone backed away from the larger pile. "Or it has to be confined, in a sphere or-"

The loudest explosion of all tore the air, making everyone stagger. The adults looked at each other, horrified, then turned their eyes south. A column of smoke boiled into the air south of the Water temple.

"One of them hit," Lark whispered.

Rosethorn turned and raced into the cottage. Briar followed her.

"The carpenters' shops," said Gorse, his deep voice hushed. "All that wood - the glue, the varnishes-"

"It'll burn fast and hot." Frostpine made the G.o.ds-circle on his chest.

Tris was trembling so hard that her teeth were clicking. Where would the next stone fall? The image of the destroyed galley rose in her mind, a warning of the fate of any struck by these ugly new weapons.

Lark turned to the four. "You are to stay right here." They had never heard her this stern. "Don't stir outside our fence.

We're going down there to help - I don't want to have to worry about what you're up to."

"Can't we help?" begged Sandry.

"No. No. There are plenty of adults trained to handle things like this. I won't have you exposed unless it can't be avoided."

Rosethorn came out, lugging a heavy basket. Briar was behind her with another.

"Can't I please go?" he asked as Frostpine took his burden.

'No, you may not" snapped Rosethorn. "You'll stay here -all of you!"

Without another word, the adults ran through the gate and down the spiral road. Little Bear sat on his rump and, began to howl.

Three more boom-stones exploded overhead. Tris flinched at each one; her hair began to rise and crackle. She tucked her hand into her pocket, and rubbed Aymery's earring.

They had to distract Tris, before something else happened, thought Daja. "What if you tried your lightning on that?" She pointed to the heap of black powder that lay forgotten in the path.

Tris stared at it. "I - I don't know," she said, her voice trembling.

"Well?" Sandry nudged.

"What lightning?" Briar demanded, sarcastic. "She's just got the worst case of Runog's Fire I've ever seen, is all."

Daja knew the pale fire that played on ship masts and tower roofs in storms as well as he did. "What she's got is seed lightning," she returned. "It's not the same. Show him, Tris."

Another boom-stone exploded over the Hub. "I c-c-can't," Tris replied, shivering with fright. What did they want from her? Couldn't they see that each explosion felt like a sharp blow to her? Her muscles were clenched, awaiting the next strike, and her neck and back were aching.

"Don't you have to learn control?" Sandry asked. "No matter what else is going on?

Maybe this is a good time to practise."

Tris glared at the other three, hating them for bothering her. She just wanted to run inside and hide under a bed.

"Ahhh, I knew it," Briar remarked scornfully. "It's just Runog's Fire."

Furious, Tris pointed to the heap of powder a foot away. Lightning jumped from her finger. There was a clap: dirt and smoke sprayed everywhere, blackening them and turning the observing Little Bear grey. The dog yipped, and fled into Discipline. The four looked at each other, eyes wide in soot-streaked faces. There was now a hole in the path.

"You see?" Briar said at last. "You just have to know what to say to her."

"You-" Tris snapped, and pointed at him without thinking what might result.

Briar grabbed her arms, hard, shaking her as lightning-sparks raced over his hands.

"Don't you ever do that," he whispered, his eyes burning into hers. "Don't you ever.

If your pointing is a weapon, then don't you point 'less you're ready to kill with it.

You understand, you witless bleater?" He was so frightened he didn't know where his trembling ended and hers began. "Niko's right." He let her go and pushed her away from him. "We got to learn control, and you most of all."

"I'm sorry." Tris's eyes were spilling over, but she made herself look Briar in the face. "I'm sorry. I didn't -I wouldn't ever-"

Sandry put her arm around Tris's shoulders. "We can't just act without thinking any more, Tris. They've been trying to teach us that all along. I guess if we're mages, we can't exactly be kids, can we?" she asked the other two. They shook their heads.

"Briar knows you would have been sorry after."

"After I was a nice crispy roast just off the spit," the boy said cruelly.

Tris hid her face in her hands.

"Enough," Daja said. "She got the point. Don't bully her."

I'm a scared bully, thought Briar, stuffing his hands into his pockets. And I want to be sure she's scared, scared enough to think next time.

Tris yanked out of Sandry's hold and ran up to her room.

Briar went to examine the miniature pine tree that sat on his window-ledge, letting the shakkan's years and plant-calm steady his nerves. Checking the dirt in its shallow basin, he decided it was a bit dry, and went inside for water.

Daja and Sandry stayed where they were, staring at the hole in the ground.

"What do you suppose her reach is, with lightning?" Daja enquired. "Could she hit a boom-stone?"

Sandry tugged one of her braids. "I don't know. Remember the day we all first met?

Lightning struck a tree outside Administration when we were there. I think that was her -she was angry; I could tell the moment I laid eyes on her. And she wasn't excited by lightning hitting so close to her. But it was stormy that morning. This lightning just seems to cling to her - it's not part of a storm. It might not reach as far."

"But when she holds on to it, it grows. Remember? It starts as a spark. Then she holds it, and it grows into a strip." Daja scuffed at the dirt around the hole.

"/ think we should find out how far she can send it."

Sandry bent down and petted Little Bear, who had crept out of the house again. "I think you're right," said Daja.

The safest place appeared to be the lee of the northern wall beside Discipline. There was a broad strip of gra.s.s with no other plants growing there - Briar had refused to allow an experiment anywhere in Rosethorn's garden. Only the sentries could see them, but for the most part they were looking out to the north, or to the south, where the burning buildings were. By now the word had come up the road: a boom-stone had got through the magical barriers, exploding in one of the large buildings that housed Winding Circle's carpentry shops. There were dead and wounded, and people trapped inside. It would be a while before their teachers could be spared from rescue work.

Once Briar had been converted to the idea of lightning experiments, he made some reed circles for use as targets. Sandry dug in Lark's sc.r.a.p bag, and brought out a number of cloth patches which she placed in different spots. Daja's a.s.signment was to get Tris to go along.

"I think this is stupid," Tris informed them when Daja brought her to the spot they'd prepared. "I can only do it when I'm upset."

"It's magic, it's there all the time," Briar told her impatiently. "Stop it with the lady- like whining. 'Oh, I can't, I have to be scared.'"

Tris glared at him. "Why can't you let me alone?"

"Because I'm tired of living with a merchant sniffer!" he told her. "Rosethorn's out there putting healing in potions, and she's been doing it every day since the quake-"

Tris pointed at a swatch of cloth two feet away. Lightning stretched across the gap between her and the patch, but didn't touch it.

"You need me to go on carping?" Briar asked. "I've got plenty more to say-"

"You aren't always fun to live with, either, you know?" Tris snapped. She called the lightning back. For a moment she stood very still, eyes closed, breathing deep. She pointed again.

The bolt left a scorch mark on the cloth.

"Got to do better than that," said Daja, shaking her head.

"I'd like to see you try," muttered Tris. She wrapped her free hand around Aymery's earring, and pointed. The patch evaporated in a plume of smoke.

"I shouldn't have used silk," whispered Sandry. "It goes up so fast."

Tris pointed to the wall, five feet in front of her, where another patch was fastened to a c.h.i.n.k in the mortar with a thorn. Lightning stretched across the distance, but only halfway.

"Something closer," said Daja. She tossed a cloth patch several inches beyond where the first had been.

An hour later there were scorch marks on the wall, and Tris had to feed her nestling.

When she returned, she brought him with her, and gave his nest to Sandry to hold.

"He's supposed to be kept quiet," she said. "I guess there's no chance of that now."

The boom-stones had been exploding overhead off and on all afternoon.

Sandry peeked at the bird, and stopped Little Bear from trying the same thing. "He looks all right," she told Tris. "He's not shaking. I've been meaning to ask, what have you got in your pocket? You keep fiddling with something."

Grimly Tris held up Aymery's earring. "It helps me concentrate."

Sandry turned her head to order Little Bear to stop chewing on gra.s.s and halted. Light flickered at the corner of her eye, light that was not one of the other children. "That earring is magicked," she said, shocked. "And what's that thread coming out of it?"

Tris looked sidelong at it. "You're right about the magic. Aymery told me the pirate mage created it, as a bond to enslave him. I don't see a thread, though."

"It's there, heading off" - Sandry pointed due south -"that way."

Daja squinted at the earring. "I see a ghost of a wire," she admitted. "But I never noticed it before. Just that blasted flickering."

"Blame Niko," protested Tris. "I never thought that seeing-spell would cross between us like it does."

"I bet the thread is the magic bond. It goes to that mage -Enahar? Stupid name," said Briar. "Too bad we couldn't send him a little lightning, by way of it."

"It would have to go through buildings and the wall," Daja pointed out. "I don't believe it would get there."

"Let's try something more fun," Briar said, holding up a reed circle. "Tris, get one of these while they're in the air."