While the Flash and Team Arrow closed the dimensional rift looming over Central City, they still have plenty of chaos to deal with: Cisco and Curtis are lost in time, thousands of speedster refugees are now stuck on their earth, and a mad bomber is at large. But when Anti-Matter Man arrives on Supergirl's doorstep on her home of Earth-38, it'll be all hands on deck for a team-up of epic proportions to stop him.