Quinn Russell is the leader of a group called The Problem Solvers. The group consisted of Tokyo, Blaine, Quinn, and Eli, four elementary schoolers that wanted to solve various mysteries in the small town of Winston Wells. When Quinn's babysitter gives her the idea to broaden her group and solve bigger mysteries, Quinn is uncertain, but she goes along with it, because she figures it will ultimately benefit her group.

Since Quinn plans to take on the mystery, she learns about the potential case. A dog named Lemon went missing, and her owner, Ms. Dune, needs The Problem Solver's help. While the rest of her group seem excited to take on the case, Quinn worries that her dad may not approve of the new direction her group is going in.

If she didn't already have her hands full, Quinn is thrown in the middle of a feud between her two friends and a girl named Amanda Sears. She seems sweet to Quinn, but Tokyo and Blaine, her two best friends and also members of The Problem Solvers, seem to have their own issues with her. Things take a turn when Quinn is invited to Amanda's birthday party and somehow ends up working on a project with her.

From solving new mysteries to potentially making new friends, Quinn has to adapt and figure out what's going on in Winston Wells before the mystery and drama crumble her group forever.