The subject is time. Cosmic Boy, Saturn Girl and Live Wire are traveling through it. Brainiac 5 and Invisible Kid penetrate some mysteries about it, and some surprising characters pop out of it!
Members of the Legionnaires, including Cosmic Boy, Saturn Girl, Live Wire, Apparition and Triad, discover anomalies in their time period, including different team members and members who others believe are dead but shouldn't be. Invisible Kid and Rond Vidar, Brainiac 5's scientific assistant, appear to understand what's going on but refrain from telling anyone.