Oliver learns that Malcolm Merlyn is alive -- and thinks he was responsible for Sara's death; Laurel avoids Nyssa, believing that Sara's association with the League of Assassins led to her demise.

When Felicity determines that Thea is in Corto Maltese, Oliver intends to bring her back home; Diggle is double-crossed; Laurel and Ted Grant meet.

Another archer comes to town and targets businessmen; Roy is forced to tell Oliver why Thea left town; Laurel considers sharing a secret with Lance.

With crime at an all-time low, Oliver lets his guard down and is taken by surprise by a new villain; Oliver and Roy take on the Count; Diggle becomes a father; Lance gets a promotion; Laurel joins the inner circle.

Oliver is forced to reconsider what he is willing to do to stop Slade from killing someone else close to him; Diggle goes after Amanda.

As Slade's soldiers target the city, Oliver rallies his team; Felicity receives game-changing news from S.T.A.R. Labs; Thea and her father come face to face.

Diggle and Felicity go to extremes to keep Oliver from surrendering to Slade; Thea thinks about leaving town; Laurel goes after Sebastian Blood again.

When the mirakuru sends Roy into a blind rage, Oliver must find a way to stop him; Thea tries to lure Roy in by going on camera at Moira's campaign.

An epic battle ensues when the team find Slade waiting for them in the lair; Thea reaches her breaking point; Laurel struggles with a secret.

The repercussions are massive when Slade makes a move against Oliver; a key player in Oliver's team starts to question his decisions.

Oliver expects the Huntress (Jessica De Gouw) to return once her father (Jeffrey Nordling) is arrested; Laurel is involved in a hostage situation at the courthouse; Roy tries to keep Thea safe.

Oliver prepares for battle with his former friend Slade; Amanda recruits Diggle to stop a warlord, but he is surprised when he meets the rest of the team she has assembled.

Oliver is stunned when he discovers that Slade is in Starling City; back on the island, Sara and Oliver form a plan to deal with Slade's growing Mirakuru-induced rage.

Felicity feels left out when Oliver makes Sara a part of the team; a brilliant thief known as The Clock King arms himself with technology that can open bank vaults; Laurel refuses to attend a party for Sara.

Lance and Oliver try to talk Sara into reuniting with Laurel, who continues to unravel; Dinah is kidnapped.

Arrow offers to train Roy, but Roy refuses unless Arrow reveals his true identity; Malcolm's earthquake machine is stolen by the Bronze Tiger; Laurel spins out of control after she is disbarred.

Oliver feels conflicted when Laurel asks the Arrow for help investigating Sebastian Blood; Sin wants Roy to test his new super-strength.

Arrow tries to stop a man from setting off a bomb at a rally but gets trapped in the process; Thea witnesses Roy's superstrength and demands answers.

Central City police scientist Barry Allan investigates a seemingly impossible robbery; Sin turns to Roy for help when a friend goes missing.

A mysterious illness impacts hundreds of people in the city, including Diggle; Oliver realizes The Count (Seth Gabel) has escaped from prison.

Oliver learns that a man is transporting illegal guns into the Glades; Felicity shares stunning information with Oliver; Donner asks Laurel out.

At 11, Barry Allen's life changed completely when his mother died in a freak accident and his innocent father was convicted of her murder. Now a crime-scene investigator, his dedication to learn the truth about his mother's death drives him to follow up on every new scientific advancement and urban legend. When his latest obsession -- a particle accelerator heralded as a world-changing invention -- causes an explosion, it creates a freak storm and Barry is struck by lightning. He awakes from a coma nine months later with the power of superspeed. When he learns that others who have gained powers use them for evil, he dedicates himself to protecting the innocent, while still trying to solve the older mystery.

At 12 years old, Kara Zor-El escapes doom on planet Krypton to find protection on Earth with the Danver family, where she grows up in the shadow of her foster sister, Alex, and learns to hide the extraordinary powers she shares with her cousin, Superman. Now an adult living in National City and working for media mogul Cat Grant, Kara finds her days of keeping her abilities a secret are over when super-secret agency head Hank Henshaw enlists her to help protect the city's citizens from threats. Finally coming into her own, Kara must juggle her new responsibilities with her very human relationships.

Jim Gordon is a rising detective in corrupt Gotham City, where his late father was a successful district attorney. Brave, honest and determined to prove himself, Jim hopes to return the city to the glamorous, purer version he remembers as a child. He and his partner, legendary Detective Harvey Bullock, must navigate the dirty politics of Gotham's justice system, even as they tackle a high-profile case, the murder of billionaires Thomas and Martha Wayne. Gordon becomes a friend to their young orphan, Bruce.

CW and Greg Berlanti expand the footprint of their DC Comics universe with this exploration of the intersection between family life and being a superhero. As a younger man, Jefferson Pierce donned the suit of a vigilante and protected the streets of his city, but he believed he'd left those days in the past. He learns that life doesn't always work out as planned when his daughter, Jennifer -- a star student who is determined to achieve justice at any cost -- gets recruited by a street gang. In order to protect his family, Jefferson sees no choice but to once again become Black Lightning.

When over-achieving medical resident Liv Moore attends a party that turns into a zombie feeding frenzy, she ends up joining the ranks of the living dead. Determined to pass as human despite her pale appearance and newly listless demeanor, Liv forms a plan to resist her drive to consume fresh human brains by taking a job at a coroner's office, where she can secretly snack on the brains of corpses delivered there. Soon discovering that she absorbs the memories of those she feeds on, she finds new purpose by posing as a psychic and working with a detective to help solve their murders.

Phil Coulson (Clark Gregg, reprising his role from "The Avengers" and "Iron Man" ) heads an elite team of fellow agents with the worldwide law-enforcement organization known as SHIELD (Strategic Homeland Intervention Enforcement and Logistics Division), as they investigate strange occurrences around the globe. Its members -- each of whom brings a specialty to the group -- work with Coulson to protect those who cannot protect themselves from extraordinary and inconceivable threats, including a formidable group known as Hydra.