Cosima is forced into an alliance with Susan Duncan when an old enemy returns to the Island. Meanwhile, on the mainland, Krystal stumbles onto a vital clue to the Neolution endgame.
While Sarah and Kira spend time at home bonding, Cosima unlocks the island’s biggest secret, discovering a link between the village’s so-called creature and the science around Kira.
Oliver assembles a group of unlikely allies – Slade, Nyssa, Merlyn and Digger Harkness – to engage in an epic battle against Chase and his army
Black Siren returns to give Chase help; Felicity plans a birthday party for Oliver; Lance is angry with Rene for missing the custody hearing about his daughter.
Oliver faces the forced release of criminals prosecuted by Adrian Chase, while a crate is delivered to Oliver’s office containing a corpse in concrete.
Oliver and Felicity get trapped in the bunker together, while Diggle and Lyla deal with marital issues.
Oliver, Team Arrow, ARGUS and the SCPD kick off a citywide manhunt for Adrian Chase. Helix tells Felicity they have a way to find Chase but they will need something big, and illegal, from her in return.
Sarah and Siobhan follow a lead on a Neolution defector, hoping for enough leverage to free Kira from Dyad’s clutches. Also, Cosima investigates rumors about a creature in the woods.
As Clone Club reels from the loss of one of their own, Sarah gnaws at the shackles Rachel has firmly placed around her family. Alison struggles to find her place in the sisterhood.
Dragged home from the Island by Neolution, Sarah refuses to follow Rachel’s new regime. Sarah sets a plan in motion to get her and her daughter out of Neolution’s reach for good.
Desperate to get off the island and reunite with her family, a wounded Sarah journeys into the island’s interior, only to discover a mysterious village – the beating heart of the Neolution agenda.