The Lock-In was an event in Westmore Middle School where kids could spend the night and have fun. Its real purpose was to raise money for the school's music program, "Save Our Music".
In the book
Shown as a "fun" event, it was proven to be boring and risky for Greg Heffley and many other kids. Though it was technically coed, only about 10% of the students who showed up to the event were girls—also, Greg claims that were too many adults at the party, claiming that there was at least one adult for every kid that was there (most of the chaperones while the rest were teachers who Greg figures were forced to be there).
While there were activities and games set up for the students to do, they weren't really all that fun and weren't very appropriate for middle school students (the games and activities were better-suited for little kids). Also, most of the kids who went to the Lock-In brought electronics with them to keep themselves entertained, but those were all eventually confiscated by the chaperones, who forced the kids to be more "social" with each other at the party. Some of the kids also brought snacks and drinks for themselves, but those were ultimately confiscated by the chaperones as well.
One of the games that the students played was "I Never Told Anyone this Before," which Mrs. Carr claimed would help the kids bond with one another, but most kids told bad confessions about themselves. Greg knew that the purpose in THAT game was to let the chaperones know who the troublemakers were. His suspicions were confirmed when an adult trailed Teddy Caldwell who had graffitied a bad word on the school.
There was a game of Guess-Who? which involved a camera, making the students excited to use an electronic again, despite the cameras being the old-film type, which dissapointed the students. During a game of "Guess-Who?", in which the purpose is to take a close up picture of a body part of someone in their team and then the other teams have to guess who is in the picture, Greg's team took a picture of Tyson Sanders's bent arm. They had the best picture of the teams but they got into near trouble when a chaperone confuses it for someone's buttocks. When Greg's team members make a run for it, they are all eventually caught except for Christopher Brownfield. However they were able to get the teachers to believe it was a bent arm and were let off the hook.
During the night, the boys made fart noises and were still awake. Mr. Palmero turned off the heating to keep them in and told them to fart behind the curtains, which caused major disturbance. At around 3 AM, a group of angry parents pounded on the doors, as they were worried about their kids—as it would seem, these parents tried calling their kids on their phones, but since the chaperones confiscated them, the kids weren't able to get in touch with their about what was going on.
As Greg and Rowley were the only kids at the Lock-In who didn't have their own cellphones, they were the only ones left once the group of angry parents took their kids home. Greg later thinks that the whole reason the Lock-In existed was to turn kids off from boy-girl parties. However this does not change his view, as he is seen excited over Jordan Jury hosting a boy-girl party.
- It is unknown who went home first between Greg and Rowley.
- An event like the Lock-In would be illegal in real life.