Oliver hunts down a drug dealer known as "The Count" to prevent the distribution of a new drug known as Vertigo... after Thea has been arrested for using it. While Oliver turns to a former girlfriend and current vice cop for help, Moira defends Thea and Felicity learns more about Moira.moreless
The fate of humanity is on the line as Walter plans to make the ultimate sacrifice to stop the Observers before they were ever created.
To penetrate the Observers' headquarters and rescue Michael, their only hope for victory, Olivia must use her abilities and meet with some old friends.
Oliver learns that he is not the only person in Star City that is flying under the radar of the police. An assassin named Deadshot is targeting businessmen bidding on an energy project, and Walter is one of the men involved. Oliver has no choice but to turn to Detective Lance for help to protect his family while he taken on the killer.moreless
Ray and Tammy's wedding day arrives, but their ceremony is interrupted when Mitch is kidnapped outside the church. While captive, Mitch hears his captors speaking in Russian and comes to the conclusion that the elaborate frame on Patrick Walker must be a part of the war against the Morolto family. Despite the danger his family is under, Joey insists Mitch honor their deal on the understanding that his family will protect them.
The dying Observer comes to see Walter and Peter, who must take extreme measures to learn what secrets he hides and determine if he knows where Olivia is. Meanwhile, David Robert Jones tries to force Olivia to use her cortexiphan abilities by torturing Nina.moreless
While Peter and Olivia investigate murders involving an inexplicable toxin, Astrid and her Other Side counterpart meet for the first time.
The teams on the two worlds work together to solve the case of a shapeshifter, and Agent Lincoln Lee joins his world's team when no one remembers the existence of Peter Bishop.