Xia Tian, Jia Jiang, Fang Wei, and Bulu grew up on Westside Street together and currently study at Ying Ye School. It's one month away from graduation. Xia Tian's dad is a police officer on Westside Street and is retiring. But on the day of his retirement, the kids had a fight with the Dinosaur gang at school and were almost expelled. When Officer Xia went to settle the conflict, his gun was misplaced by the principal. After a discussion, it was decided that the students would remain in the school, but they must find the gun within the one month before graduation to let Officer Xia retire peacefully and happily. While searching for the missing gun, they discovered that an ex-convict Grey Wolf who escaped from prison may be connected with the missing gun. And more surprisingly, Grey Wolf is has been in close with the students at Ying Ye.