The series follows Oliver Queen (Stephen Amell), billionaire playboy of Starling City, who spends five years stranded on an island following a shipwreck that claims the life of everyone else on board, including his father, Robert Queen (Jamey Sheridan). Upon his return to Starling City, he is reunited with his mother, Moira (Susanna Thompson), her new husband, Walter Steele (Colin Salmon), the then-current CEO of Queen Consolidated; and his younger sister, Thea (Willa Holland). His best friend, Tommy Merlyn (Colin Donnell), the son of billionaire Malcolm Merlyn (John Barrowman), and ex-girlfriend Laurel Lance (Katie Cassidy), also greets him. The series also features the introductions of various DC Comics characters, both in present time and flashbacks to the island, many of whom are vying for control of Starling City.
The first season focuses on Oliver reconnecting with people upon his return, and spending his nights hunting down the wealthy responsible for "failing the city" as a hooded vigilante who is not afraid to kill his targets. He becomes at odds with a secret organization that plans to destroy the Glades, a section of the city that has become overridden with crime. John Diggle (David Ramsey), who acts as Oliver’s bodyguard in front of the public, and Felicity Smoak (Emily Bett Rickards), an IT specialist who works at Queen Consolidated, assist Oliver in his crusade. The first season also features flashbacks to Oliver's time on the island, and how it changed him; this continues in the second season.
In season two, Oliver is driven to stop crime without killing criminals, motivated by the death of his friend Tommy. His newfound ideals are consistently challenged by his enemies however, not least of them Deathstroke (Manu Bennett), whose vendetta against Oliver thrusts Starling City into chaos and forces him closer to crossing the line between hero and killer. Oliver must also contend with outside forces attempting to take over Queen Consolidated, and continued revelations of his own past, as well as those of his family and friends. In time, Oliver accepts aspiring vigilante Roy Harper (Colton Haynes) as his protégé, and begins to receive assistance from Laurel's father, Officer Quentin Lance (Paul Blackthorne).