Slade returns and asks Oliver for help in tracking down his son. When they learn Joe has been taken hostage by mercenaries, their mission to save him gets complicated by a terrible revelation that could shatter Slade's hopes of reunion forever. Meanwhile, Vigilante reappears in Star City.

As Slade continues to uncover clues about his son’s last few years, Oliver makes a big decision. Meanwhile, the Green Arrow leads the team into battle against “The Dragon,” a villain who is stealing valuable tech in Star City.

With Oliver and Barry still stuck in the other’s bodies, the two get a lead on John Deegan and head to Gotham City with Supergirl to figure out why their reality has changed. While there, they meet the mysterious Kate Kane who provides them with information that leads the group to Arkham Asylum.

The crossover starts on The Flash S05E09 Elseworlds (I) and concludes on Supergirl S04E09 Elseworlds (III).

The past comes back to haunt both Oliver and Laurel. Curtis is upset when he discovers that Diggle and Lyla have restarted The Ghost Initiative with Diaz, China White, Kane Wolfman and Carrie Cutter.

After months of covertly pursuing Dante, Diggle and Lyla finally have a solid lead on the elusive terrorist, so they deploy the ARGUS Ghost Initiative to apprehend him. Meanwhile, Oliver tries to bond with Emiko.