With a half-blink's time of thought, he explained about Tris's magicked spectacles, and the silver glitter of magic that the four children now saw. They broke through the wall, and the earth outside the wall, and the spells that held the ground under Winding Circle together. They were in soft dirt now, spreading themselves wide through the slope down to the water.

The seeds were on the surface. Rosethorn called to them, breaking into hundreds of magical threads, each seeking, then entering, a seed. In her magic was the power of stone-cracking vines, of pine seedlings that could grow over a farm in a handful of years, mixed with the demand for haste that only humans felt. Briar saw how she made her magic a root system; all that was left for the seeds to do was to stretch out branches and limbs, instead of fragile shoots. Once he knew what he saw, he reached with his magic, running it through the pattern she had placed inside him. Connecting to hundreds of seeds to her left, he fed them a rush of strength. Bushes and brambles leaped into growth, exploding from the ground, throwing out leaves and flowers as if a spring were compressed into minutes.

Rising above the ground for a look, he discovered his third of the barren slope was covered with the fresh, pale colour of new growth. Rosethorn had two-thirds of the open ground; her plants were dark green, the thistles already a foot high. Her vines and brambles scrambled to cover as much surface as they could, reminding Briar of a litter of puppies squabbling over a meat-covered bone.

Nearby he could hear a series of dull cracks. Something thudded, shaking his spine.

Fire erupted in his shoulder and on his back - not the back of the body still up on the wall, but on his magic's back. Briar yelled, looking around. Five more craters had been gouged out of the earth. They smoked and glowed like dying embers, filling the air with the stink of burning leaves.

He could feel Rosethorn trembling behind his true body. "Concentrate!" she snapped when she realized he was thinking of her.

Briar urged his plants forwards through the magical root-pattern. He coursed along their veins, filling them with anger. Bramble wove itself into thistle clumps and braided with rosevines. Sea holly mingled with sea buckthorn to form solid walls of stickers. Moving out into the plants' skins, he gave particular attention to each and every spine and thorn, urging them to grow, and to grow sharp.

To give them fuel, he fed them his hate for pirates on shore leave who thought it fun to kick a street boy, or break his arm as a warning to pickpockets. They would wrap and cling like the muck of the sewers that he'd once lived in. Emotion ran through his garden like sullen blood, a dose of misery, resentment and fury that they would be eager to pass on.

More cracks; overhead, boom-stones bounced off glowing circles in the air. The circles turned and shifted as the mages used them like shields to keep boom-stones off Winding Circle. Once a ball was knocked from its path, it either blew up - or fell.

Six roars shredded the air as four boom-stones exploded high overhead. Near the base of the wall two fountains of dirt and rock erupted, spraying everyone above. Rosethorn and Briar screamed in pain and rage as their greenery was torn to oozing pieces.

"Look at the shore. Can you speed it up?" Skyfire asked, his voice booming in their bodies' ears. Sending their power above-ground, Rosethorn and Briar looked at the water's edge. The longboats had reached the shore. Three-foot-high plants awaited them where Rosethorn had been working; Briar's were a little more than two feet tall. It wasn't enough to stop them, not for long.

"Deeper," Rosethorn growled. "I'm going deeper into the spell."

"I don't know how," Briar reminded her. "Show me."

"No. Keep working as you have. You aren't ready for this."

Somehow she moved him, until his pattern fed into the plants she had brought along already. Part of her remained there, while the rest wove itself into Briar's old area. She flexed around him, then pulsed, expanding like a bursting sun. Where he had gone only as deep as each plant's skin, keeping most of his attention for their weapons, Rosethorn became each and every root and stem. She collapsed the growth of months, even years, into a breath. Everything grew.

It was a comfort to find that her thorns, needles and stickers weren't as long or sharp as his. She didn't hate enough, he decided. She had never been tossed through the air by pirates celebrating a big haul, or dropped because they were too drunk to see where she was thrown. Briar shared that with her plants as their leaves and stems lengthened. Their spines stretched for him, looking for a pirate to sink into.

Something louder than the earlier boom-stones whooshed through the air, near enough that his real body flinched. There was a dull thud, and a sudden wash of heat. Briar threw up an arm to shield himself - to shield his plants - from the fire. Rosethorn screamed, and screamed again.

The raiders had landed. Setting up catapults, they had launched skins of battlefire into the green tangle before them. On landing, the skins had burst, spraying jelly everywhere. The mages had only to touch the stuff with flame to make it burn. Sheets of fire sprouted between the raiders and the wall.

Nearby, someone was screaming. Further down the wall, a gout of battle-fire had splashed through the mages' protections. A warrior-dedicate stumbled burning through a notch and fell into the brambles. Other dedicates were beating out flames with their habits. Two novices dragged a charred body out of the way. It looked like the woman warrior from that morning.

Rosethorn sagged against Briar. He dragged her arms around him, taking her weight on his shoulders. She was groaning deep in her throat. Suddenly, he was terrified. Sandry! Tris! Da -