On school picture day, Nick and his friends make another plan involving the word "frindle." They whisper the plan to all of the other kids, who agree to play along.

The photographer lines up the class for a group photo. He tells everyone to say cheese, but nobody does. Instead, they say, “Frindle!” They all pull out frindles and hold them up to show the camera. The photographer has no more film, so he cannot take another picture. The frindle picture will be the permanent record of Nick’s fifth-grade class. All the teachers are angry about it, especially Mrs. Granger.

The next day, Mrs. Granger puts a note on the bulletin board:

Anyone who is heard using the word frindle instead of the word “pen” will stay after school and write this sentence one hundred times: I am writing this punishment with a pen.

The kids think using Nick’s word is fun, and Mrs. Granger’s note just makes them want to use it more. Pretty soon, people start thinking it is cool to get put in Mrs. Granger’s anti-frindle detention.

One day, Mrs. Granger tells Nick to come see her after school, just to talk. Nick thinks this is pretty exciting. To him, it’s like a discussion between generals of opposing armies during a war.

In their conference, Mrs. Granger tells Nick that his frindle game has gone far enough. Nick explains that he is not trying to do anything bad, but that he thinks saying "frindle" is fun. He points out that Mrs. Granger was the one who said words change because people decide to change them.

Mrs. Granger says that this is true, but she still does not think pen should be replaced by a silly word like "frindle." She tells Nick about word histories and explains that "pen" comes from the Latin word "pinna."

Nick does not back down. “But frindle makes just as much sense to me,” he says. Mrs. Granger gets an angry look in her eye and asks Nick if he is refusing to back down. Nick explains that he cannot back down, that he and his friends took an oath to use his word.

Mrs. Granger shows Nick an envelope containing a letter she has written to him, but she does not let him read it. She makes Nick sign and date the back of the envelope. She says she will give him the letter only when the frindle business is over, and his signature will prove to him then that she has not changed her words. Nick thinks this is pretty weird, but he cannot see the harm in doing what Mrs. Granger says.

Afterward, when Mrs. Granger sends Nick on his way, she looks happy. “May the best word win,” she says.

The next day, Nick and his friends get the whole fifth grade to ask Mrs. Granger for a frindle. Almost eighty kids have to stay after school for detention. The day after that, much of the rest of the school joins the fifth graders. Almost two hundred kids get detention.

Nick’s whole school is in an uproar. Parents are upset. Bus drivers threaten to strike. Even the school board is busy talking about Nick and his frindles. All of it means trouble for Nick.