As the day dragged on, the tension inside Truthful began to build. She began to prowl restlessly about the house, until Lady Badgery emerged with fez on head, and insisted that they play cards until it was time to begin their preparations for the masquerade ball.

Being in Brighton, the ball started early, at eight o’clock. Truthful, Lady Badgery and Lady Otterbrook took supper together at six. They spoke little, and Truthful spilled her wine. She was glad when it was over, and they could go up to dress.

Coming back down shortly before half past seven, she saw Charles already below so she paused on the stair. This time, she caught the light perfectly, the red-gold rays of the setting sun making her white and silver costume flash and her red hair looked as if too was aflame.

Charles looked up and caught his breath, shading his eyes as if blinded by an actual goddess. As he was in costume as Hermes, himself clad in a golden raiment with wings on his boots, this looked rather theatrical and made Truthful laugh.

“You are a lovely Diana,” said Charles, taking her hand. “Have you tested your bow?”

“And you are a handsome solar messenger,” replied Truthful. “As for the bow, I have put several holes in the wall at the end of the corridor opposite my room. It shoots well enough and the arrows have actual points. Great-aunt’s Turkish knife is in my quiver as well, and I am wearing your bracelet.”

“Aunt Lucy’s bracelet, in fact,” said Charles. “She was kind enough to lend it to me.”

“Oh,” said Truthful. “I wish I had known! I must thank her.”

“She will be down soon, I am sure,” said Charles. “Aunt Lucy is never late, and she must be first to greet the guests. Though Uncle is already there, practicing with his waves.”

“Has there been any sign of Lady Plathenden?” asked Truthful.

“Not yet. Sir Everard is looking through all the guests as they arrive, piercing their glamours and costumery, so she shall not get in unobserved. Ah, here are Aunt Lucy and Lady Badgery. A pirate and a . . . I am not entirely sure . . .”

“I am the Empress Theodosia,” sniffed Lady Otterbrook, who was wearing a white toga with a purple stripe and a crenelated crown of gold set with large square gems. “I thought anyone could see that.”

“It was on the tip of my tongue,” said Charles. “Forgive me! You make a very grand Empress, Aunt. And a very bold pirate, Lady Badgery. Is that a real cutlass?”

“It is,” replied Lady Badgery. “And I had it sharpened this morning. Holds an edge like a razor, my boy. Like a razor!”

“We had best be getting along,” said Charles. “The carriage is ready.”

Though it was a very short distance to the Old Ship, it took some time to get there. The crush was not so great as for Lady Mournbeck’s ball, many of the guests choosing to walk, but there was an added delay due to the enthusiasm of the constables, who insisted on examining the interior of all conveyances, and who had already arrested three mermaids who proved to be blameless.

However, shortly before eight, Truthful, Charles and the two elderly ladies were climbing the stair to the Assembly Rooms, past the standing footmen attired as Vikings, most of whom were actually government agents.

“Those axes look surprisingly authentic,” whispered Truthful to Charles as they passed through the double doors into the main ballroom, under the musician’s gallery.

“They are,” said Charles. “Borrowed them from the Tower, General Leye brought them down this afternoon.”

“Charles,” called out Lady Otterbrook. “Go and fetch your uncle from his ridiculous corner. I need him to stand with me to greet the guests.”

“Remember, at least two dances,” said Charles, relinquishing Truthful’s arm before heading over to the far corner, where the Marquis, in a horned helmet and a bearskin was standing on his throne and gesturing at several footmen who had large pasteboard waves affixed to their backs. They were crouched down in a line, and on his signal, slowly shuffled forward and back.

“Lady Truthful, it is a pleasure to see you again.”

Truthful turned and smiled at General Leye.

“And you sir. You know my great-aunt, Lady Badgery?”

“Know him?” whispered Lady Badgery in Truthful’s ear. “We were subalterns together in the Buffs.”

“What’s that you’re saying?” enquired General Leye, with a twinkle in his eye. “Blackening my name, Ermintrude? I don’t suppose you’d care for a rubber or two of picquet?”

“I certainly would, General,” replied Lady Badgery. She looked over the ballroom. It was beginning to fill up with gorgeously costumed guests, the orchestra had begun to play and soon there would be dancing. There was no immediate sign of a malevolent mermaid or Lady Plathenden in any other garb. “Presuming we can be spared. The card tables are in the other chamber, I perceive, as usual?”

“I believe young Otterbrook has matters in hand,” said the General. “In any case, someone must watch in the card-room as well. A shilling a point?”

“Let us say sixpence,” replied Lady Badgery, taking his arm. “And a guinea the rubber.”

As soon as they had departed, Truthful was once again besieged by gentlemen hopeful to secure a dance. But to every enquiry she gave the same answer, “I am sorry, I am already spoken for, Lord Lytchett has that dance.”

Before long this response was noted unfavourably not only by the gentlemen concerned, but by several mothers of the type found terrifying by Edmund Newington-Lacy. They found common cause in quietly disparaging comments about Truthful’s character, conduct and dress and in the fact their own offspring had failed to attract Charles Otterbrook’s attention at all. They ascribed his apparent penchant for Truthful’s company not to her beauty or address, but as likely being due to the Viscount — never known as a gamester — suffering some secret loss requiring him to repair his fortune by marrying an heiress.

Truthful did not dance the first dances, because Charles was busy assisting the Marquis, or rather in encouraging him to leave his throne and his waves to join his wife in greeting the guests. Then he walked around and took part in what was hoped to be surreptitious conferences with various Viking footmen. But he returned to Truthful for the first waltz, and took her in his arms as the music began. They danced in silence for the first few bars, Truthful counting her steps until she relaxed in the knowledge that she did know the dance, and Charles would successfully lead her anyway.

“Any sign?” she asked softly, as they twirled near the deserted Canute’s throne.

“No,” replied Charles worriedly. “We’re up to six mermaids arrested now, but none of them are her. It may be as well she doesn’t turn up after all. Sir Everard says the Emerald is definitely Canute’s Valdbjarg. Or rather, his wife Aelfgifu’s Valdbjarg.”

“What does that mean?” asked Truthful.

“Sir Everard says the closest he can make it is ‘power-stone’,” said Charles. He was looking over her head, eyes flickering about the crowd. “Which does not sound at all as if the only thing it can do is make or quell storms.”

As he spoke, the music suddenly faltered, with the shriek of a violin bowed wrong. Charles instantly swung Truthful to the wall and they turned together to look up at the musician’s gallery.

A tall, striking-looking man in the ordinary rather drab evening clothes of a working musician let his violin fall, stood up from the seated musicians and moved to the railing of the gallery. The conductor there gestured violently with his baton.

“You! Take your seat at—”

He never finished. The tall man plucked open his coat and tore away his neck-cloth, and the ballroom was suddenly filled with an eldritch green light that emanated from the brilliant emerald he wore on a silver chain about his throat.

As the light spread, all movement stopped. Truthful felt the power that came with it grip her every muscle. Her hand, already to her shoulder, reaching for an arrow, was held motionless. She saw Charles’s fingers caught at the opening in his tunic, no doubt reaching for a pocket pistol he could not remove or point.

“Welcome to my masquerade!” declaimed the man, but it was not a male voice. It was higher and piercing: the cold, heartless voice of Lady Amelia Plathenden. “Do not fret! I shall not keep you long. And when we go, we shall all go together. Yes, all of you, who would not grace my parties, who cut me in the street, who would not grant me vouchers to Almack’s! Who killed my husband! Even the fat prince, thinking himself safe in his dwarfish palace. He will go with me too. You will all go with me.”

A chill breeze came with her words, making the candles flicker in the candelabras high above, and the music in the stands blow off the stands and scatter down like leaves, the only movement in the silent, motionless ballroom.

But it was not the breeze that chilled Truthful’s heart. The breeze was only a small harbinger of what Lady Plathenden had truly wrought. Truthful could feel it through her bones, sense it building to the south. For now, it was far off, gathering size and strength. But all too soon it would begin to move.

Lady Plathenden was using the Emerald to conjure a giant wave.

A wave that would come crashing down upon Brighton. A vast wall of swift water, towering higher than the clouds, it would demolish the grand houses on the Marine Parade, the humble fisherman’s cottages to the west, the shops and dwellings in the narrow lanes.

The great wave would smash the Assembly rooms of the Old Ship to pieces and sweep the Marine Pavilion away, iron framework and all.

As Lady Plathenden said, they would indeed all go together.

Everyone, from the Prince Regent to the humblest fish-wife.

All would be killed.

Truthful thought of Charles, and his fear of drowning, and resolved that it would not be so. She looked up at Lady Plathenden and saw her outline shiver. In the green light of the Emerald she looked less and less like a man and more like a woman uncomfortably in male clothes. Truthful narrowed her eyes and concentrated on the Emerald.

You should not be doing Lady Plathenden’s bidding, Truthful thought fiercely. You should be doing mine! Let me move, for you are my Emerald, as you were my mother’s, and my grandmother’s, and so many mothers and grandmothers before them, back to Aelfgifu and beyond. You are mine to command!

“What?” asked Lady Plathenden, apparently of the empty air. She looked down, searching for Truthful. Her head moved from side to side as she gazed into the crowded dance floor, a sea of statues, of popes and kings and queens and gods and goddesses. All masked, disguised, unable to be identified.

Truthful felt a warmth in her fingers, a tingling in her arms, and knew that she could move again. She no sooner felt it than she did so, drawing an arrow from her quiver with one swift motion, setting it to her bow and drawing the bowstring back.

The movement caught Lady Plathenden’s attention. She reached for the bone wand, smoke already trailing from her fingers, a spell begun.

But it was not completed.

Truthful’s arrow sped true, sprouting shockingly from Lady Plathenden’s eye, the azure fletching no longer the only piece of colour, a sudden scarlet spreading down the shaft. The glamour left her, the bone wand fell from her nerveless hand, and she toppled over the railing to crash into the floor below, between a unicorn and an unlikely cloth-of-gold clad milk-maid.

The green light winked out as if it had never been. Truthful ran to the body before anybody else could begin to move. Snatching the Emerald, she broke the silver chain and ran for the door.

“Go to high ground!” she shouted. “She has conjured a giant wave!”

Lady Plathenden might be dead, but the wave lived on. Truthful could feel it, and knew it to be moving now. It was already more than a hundred feet high, and two miles wide, and it would strike the coast in less than fifteen minutes.

She ran down the stairs, jumping three at a time. Startled Vikings clutched their axes and made slow movements as she passed.

“Get everyone to high ground!” shouted Truthful, again and again. “High ground!”

Outside, she saw her cousins and the real Major Harnett, but did not pause. They rushed to her, but she did not answer their questions, merely shouting as she ran past them towards the beach.

“High ground! Plathenden called a great wave! Go to high ground!”