Marnie swam to oceanography, thinking about Urchin. It was amazing that he had recognised her because she smelled like her aunt. She couldn’t wait to tell Christabel.

“Marnie!” Pearl was waving from the Oceanography Cave. “Mr. Scampi says a large school of blue tang is about to swim past. Come on! We saved you a seat.”

Dora and Lupita grinned at Marnie and beckoned her over to the big observation window.

Mabel Anemone was sitting alone at the front of the class. Marnie looked around for Orla, but couldn’t see her.

“What did I miss?” Marnie asked, swimming up to her friends.

“Just some boring stuff about ocean weather,” said Lupita.

“The good part’s about to begin,” said Pearl eagerly. “We have to count the blue tang when we see them.”

A large black lobster at the front of the classroom waggled his claws at her. “Marnie Blue?” he said.

“Sorry I’m late,” said Marnie quickly, taking a seaweed scroll and shell pen out of her backpack. She hoped Mr. Scampi wasn’t another one of the teachers who hated her aunt.

Mr. Scampi flicked his antennae. “Take a seat and start counting.”

Marnie had barely sat down when there was a flicker of color outside the window. The mermaids gasped. A rippling wave of bright blue fish glided past, their fins glowing with color.

“Onetwothreefourfive,” Pearl said very quickly. “Sixseveneight . . .”

The room filled with the sound of counting voices.

“Tang are extremely poisonous,” Mr. Scampi said, raising his voice over the noise. “You are strongly advised never to eat one.”

“What’s the difference between venomous and poisonous again, Pearl?” asked Lupita.

“Shh,” said Pearl, cross-eyed with the effort of counting the tang. “Seventeeneighteennineteen . . .”

“You can eat venomous fish but not poisonous ones,” said Dora. “I think.”

Marnie counted twenty-five tang and then lost her place. “Where’s Orla?” she asked Lupita, who had given up at eleven.

“Don’t know, don’t care,” said Lupita.

“No one talked to her at lunch, Marnie,” Dora said, leaning in close. “Not even Mabel. Orla sat down at a table and everyone else left. Imagine!”

“Nobody likes a tattletail,” said Lupita darkly. “Orla Finnegan is a tattletail AND a liar AND a scaredy catfish for not going in the stable after you like she said she would.”

“Thirtythreethirtyfourthirtyfive,” said Pearl.

Marnie felt guilty. She didn’t like the thought of anyone sitting alone in the Dining Cave. Not even Orla Finnegan.

“But lunch was ages ago,” she said. “Why isn’t she in class?”

“Fifty-three!” Pearl shouted as the last tang swept past. Everyone else had stopped counting. “There were fifty-three, Mr. Scampi.”

“Excellent,” said Mr. Scampi. “Write it down.”

Lupita wrote “fifty-three” in large curly letters on her seaweed scroll. “Good riddance to bad oysters,” she said. “I don’t care if I never see Orla Finnegan again.”

Marnie invited Pearl, Dora, and Lupita back for dinner after school, but only Pearl could come. The others made Marnie promise to invite them another time, and swam home reluctantly in the opposite direction.

“Don’t you think it’s weird that Orla wasn’t around this afternoon?” said Marnie as she and Pearl skimmed along, enjoying the feel of the cool water on their tails. “So far, she’s usually sat at the front and sucked up to teachers. Even with everyone giving her the silent treatment, she wouldn’t skip class.”

“She was there for the start of oceanography, when Mr. Scampi was talking about that hurricane,” Pearl said. “I saw her by herself at the back.”

“What hurricane?” said Marnie.

“Oh! I forgot you missed that part,” said Pearl. “There’s this really bad hurricane that’s just struck the Gulf of Mexico. Force nine, Mr. Scampi was saying.”

“The Gulf of Mexico?” said Marnie. “Orla’s sister works in the Gulf of Mexico.”

Pearl looked puzzled. “Oh yes. I forgot that. But why are you worried? I thought you hated Orla.”

“Orla hates me,” Marnie pointed out. “Not the other way around.”

Marnie was scared of Orla, but she didn’t hate her. Marnie wasn’t the hating type.

“I’m sooo nervous about meeting your aunt,” Pearl confessed.

Marnie pulled her thoughts away from Orla. “She’ll make you laugh as soon as you meet her, I promise,” she said. “Want to race there?”

Pearl flipped her golden tail and took off. Laughing, Marnie chased her. They ducked through the seaweed and dodged the little shoals of fish, and Pearl sneezed when she got too close to the coral reef.

Suddenly Marnie stopped and cocked her head. She could hear crying. Leaving Pearl practicing somersaults on the lagoon bed, she swam to an outcrop of coral and looked behind it cautiously.

Orla Finnegan’s eyes were as red as the coral she was sitting on. Crouching with her arms wrapped around her tail, she glared at Marnie.

“This is your aunt’s fault,” she spat. “It’s ALL HER FAULT!”

Marnie struggled to understand what Orla was talking about. “I’m so sorry,” she said, her thoughts scattering like bubbles. “I don’t—”

Orla reared up like Typhoon the seahorse. “She didn’t play my sister’s song on Radio SeaWave.” Her voice was as cold as an Arctic current. “She promised to play it. She PROMISED. Sheela was going to launch her singing career in Mermaid Lagoon. But instead she had to go to the Gulf of Mexico for work and now she’s missing in the hurricane! Your aunt’s a liar. I hate her and I hate YOU!”

And with a sob and a flip of her long purple tail, she swam away.