Ethan checked the mailbox. There were two bills, three ads, and a letter. The letter was for him!

It did not have a return address. So he didn’t know who it was from. He wasn’t sure who would write him.

Only his grandparents sent letters. And they always used the same return address stickers. The stickers had a frog in the corner.

Ethan tore open the envelope. There were two sheets of paper inside. They were both blank. Huh?

Ethan showed his parents. They called his grandparents to see if there had been a mix up. But his grandparents hadn’t sent anything.

At school, Ethan asked his friends if they had written to him. They had not. It was a mystery.

The next week, Ethan got another letter. Again it had no return address. And again the pages inside the envelope were blank.

Ethan wrote on the neighborhood message board. He asked if anyone else had gotten blank paper in the mail. No one had.

Ethan waited by the mailbox for the mail carrier. “Do you know where these letters are coming from?” he asked. The mail carrier did not.

Ethan didn’t know what else to do. So he did what he always did when he wanted to figure something out. He went to the library.

Ms. Page, the librarian, looked at the letters. “Hmm,” she said. “I have an idea.”

She showed Ethan a book about invisible ink. It said that people could write with special ink that you couldn’t see. The ink would show up if you heated the paper.

“Do you think that’s what this is?” asked Ethan.

“There’s only one way to find out,” said Ms. Page. She lit a candle and held the paper over it. “You should only do this with an adult,” she said.

Sure enough, as Ethan looked at the paper, words started to appear! Ethan read the letter. It was from his friend Mike. Mike had moved away over the summer.

“Dear Ethan,” the letter said. “I’m writing in invisible ink. Isn’t it cool?”

Yes!