In a palm tree, on an island, in the middle of the wide blue sea, is a girl.
Nim's hair is wild, her eyes are bright, and around her neck she wears three cords. One is for a spyglass, one is for a whorly, whistling shell, and the other holds a fat red pocketknife in a sheath.
With the spyglass at her eye, Nim watched the little red seaplane depart. It sailed out through the reef to the deeper dark ocean, bumping across the waves till it was tossed into the bright blue sky. Then it rose so high and so far it was nothing but a speck, and floated out of sight.
"Alex is gone," Nim told Fred.
Fred stared at the coconuts clustered on the trunk.
Fred is an iguana, spiky as a dragon, with a cheerful snub nose. He was sitting on Nim's shoulder, and he cared more about coconuts than he did about saying goodbye. (Marine iguanas don't eat coconut, but no one has ever told Fred.)
As Nim threw three ripe coconuts thump! into the sand, she remembered Alex saying, "I never knew anything could taste better than coffee!" the first time Nim opened a coconut for her.
Nim looked down at her father, sitting like a stone on Selkie's Rock. Jack's head was bowed and his shoulders slumped. Nim had never seen him look so sad.
And suddenly she knew she'd made a terrible, terrible mistake.

The mistake began when she answered Alex's very first e-mail, back when she'd thought that the famous Alex Rover was a man and a brave adventurer like the hero in the books "he" wrote. That led to Alex's ending up on the island--and when she did, Jack and Nim wanted her never to leave. Sometimes it felt good to be three instead of two.
But other times Nim wanted Jack just for herself, the way it used to be. Or she wanted Alex just for herself, because Alex was her friend before she was Jack's. Sometimes, when Alex and Jack told Nim to go to sleep while they talked late into the night, Nim felt left out and lonely.
Then, earlier this morning, the little red seaplane had arrived, bringing all the things that Alex had asked her editor back in the city to send. It was the first time a plane had ever landed on Nim's island. Nim could tell that Jack was worried that the pilot would notice how beautiful the island was and would want to come back again and again.
Whenever Jack was worried, Nim was too. And when Nim was worried, so were her friends Selkie and Fred. (Selkie is a sea lion who sometimes forgets that Nim is a girl and not a little sea lion pup to be looked after and whuffled over.) They both stuck close to Nim every time she walked back and forth between the plane and the hut.
"I've never seen animals do that before!" exclaimed the pilot.
Nim didn't know what to say, partly because she didn't know exactly what he hadn't seen before, and partly because she'd never spoken to any person besides Jack and Alex. She grabbed a crate and opened it up. Inside there were books! Thin books and fat, short books and tall, history books and science, mysteries, adventures, and more and more and more! Nim started to look through one when--
"Come on, Nim!" said Alex. "There'll be time to read when everything's off the plane."
The pilot pulled out two big solar panels. "Great!" Jack exclaimed, because he wanted them for the new room he planned to add to the hut--one created especially for Alex to write her books in. Jack balanced the panels on his head and walked very slowly and carefully up toward the hut.
"Who's going to take this one?" the pilot asked, pointing to a crate.
Nim stepped forward eagerly. But just as she was about to reach for the crate, the pilot handed it to Alex. First Alex stumbled, then she tripped, then crash! the crate fell with a tinkle of broken glass.
"Oh, no!" Alex wailed. "What have I done?"
"Jack's test tubes!" Nim shouted. "You should have let me take it!"
"I was trying to help!"
"But I didn't need help! You just got in the way!"
"I'm always in the way these days!" Alex snapped. "Maybe you and Jack would be better off without me."
"I think we would!" Nim shouted, and stomped off without waiting for an answer.
She's right! Alex thought. Nim and Jack lived here perfectly happily all those years without anyone else--they don't really need me. Nim's been cross with me a lot lately and I've never seen Jack be so worried. I think . . . I think I'm changing their lives too much. What if they've secretly been wanting their old lives back--and just haven't wanted to say so?
Alex understood about being afraid to say so. Before she came to the island, she was so afraid of saying anything to anyone that she hardly ever left her apartment. She was a famous person, but only through her books. Her life had totally changed since she flew across the world to find Nim.
"Last one!" The pilot handed her a large envelope. "And now, time for me to go."
Alex opened it. She pulled out the letter and stared at it without reading.
"Wait! Can I . . . can I go with you?"
"Sure!" said the pilot. "But don't you need to pack?"
Alex knew that if she saw Jack or Nim she would never be able to leave, even if it was the right thing to do. "No," she said, "I'm ready to go."
Alex Rover climbed into the little red seaplane. And was gone.