Frostpine, Briar and Rosethorn returned as they were starting a late midday. Everyone was glad to sit and eat. The adults passed on the information that the North Gate was closed and being rebuilt, while the spell-nets now hid Winding Circle in the north as well as the east and west.

There would be no more attacks from that direction, or so everyone had to hope. No one mentioned what would happen if the pirates were able to blast the buried spell-nets to pieces with boom-stones.

Niko arrived as they were finishing. To everyone's surprise and delight, Dedicate Gorse was with him. The stocky kitchen dedicate had brought fresh ground meat and egg yolks for the nestling, and a batch of fried sweet cakes for them to try out. He watched as Tris prepared the balls of meat-and-egg paste, and even tried his hand at stuffing two into the starling's maw.

"If we're ready?" Niko asked when the bird had settled to sleep again.

Gorse looked up at him and nodded.

"I want each of you to stand behind your teacher," Niko said. "We're going to conduct some experiments." He placed a leather bag the size of a cabbage on the table.

"What kind of experiments?" asked Rosethorn suspiciously.

Niko very carefully poured a spoonful of grainy black dust out of the bag. "We got this from the prisoners," he explained. "It's what they used to shatter the gate, and it's what they use in the boom-stones. They call it black powder. Its ingredients and the proportions are the pirate mage Enahar's secret. That's what we have to find out."

"Surely Moonstream and Skyfire -" Lark began.

"They want all the masters to try it," Niko said. "That way, everyone will have a working knowledge of the stuff. Now, dedicates, if we may begin?"

All five adults reached a hand out to the tiny pile, palms towards it. Eyes closed; when they took deep breaths, clearing their minds, the four did the same.

"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 gods-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!"