Black Siren is undercover and lures a businessman into making out with her as she is up to no good. Elsewhere, Felicity and Oliver are having a dinner while remembering their past dates.
At the bunker, the team is alerted about Black Siren's latest move and set their eyes to go after her as she killed that man. Black Siren is joined by her accomplice who hands her a folder about their next victim.
Felicity returns to the apartment and finds Alena waiting there for her. She needs Felicity's help to stop Cayden James. the founder of Helix. As she explains what he is planning to do, Felicity gets furious that Alena got Felicity involved in breaking out someone as dangerous as Cayden.
Alena explains Cayden's dangerous project and that it could result in the death of 300 million people. The team continues to look for Black Siren and what she is up to.
Felicity and Alena come up with a plan to find Cayden but Oliver shows up and is confused why Alena is there. Oliver gets the story on what is going on with Cayden and asks her to at least tell the other team members.
Black Siren sneaks up on a girl in a parking garage and presenting herself as "Dinah". The team is alerted about her movement and goes after her. They find the girl dead before Siren attacks Black Canary from behind.
Alena and Felicity go to a club to talk to one of Alena's connections, Amnesiac. They try to get information out of him but he suspects they are up to no good. A masked man storms in to save them and it's Oliver.
Felicity is annoyed that Oliver took this big risk when he currently being observed by the public. Back at the bunker, Dinah manages to find out what the three victims had in common.
Diggle gives Felicity a call to find out where she is at. She explains that it has to do with Helix, which worries Diggle. Curtis manages to track Siren's location and the team goes after her.
Felicity and Alena are trying to hack into Cayden's system but are stopped by Black Siren. A man shows up and introduces himself as Cayden. He is not thrilled with Alena's pinging his phone and orders his men to kill them.
Team Arrow shows up just in time to stop Cayden's men and another fight takes place. The battle eventually ends before they notice that Alena got shot during the fight.
Hours later, Felicity returns to the bunker and tells the others that Alena is stabilized. They keep looking for reasons why Black Siren is stealing fingerprints as Felicity connects the dots of Cayden's plan.
Felicity meets up with Oliver who heard about what happened from Diggle. She asks him how he was able to do all of this for so many years and Oliver explains he didn't have to do it alone.
Their talk is interrupted as Felicity has to take off. Black Siren and Cayden are continuing with their plan as they use the fingerprints to break into a vault.known where they plan to take down the internet.
The team arrives later to look for Black Siren and Cayden who are aware that Felicity is trying to stop the virus. He locks the system and asks Black Siren to take care of Team Arrow.
Felicity tries to hack back into the system while the others deal with Cayden's men. Oliver contacts Felicity from the bunker and tries to help her as much as possible.
Black Siren arrives and notices that something is up with the Green Arrow. He tries to fire an arrow at her, but Siren destroys it with her sonic scream.
Time is running out but Felicity manages to unlock the system and stop the virus. The team regroups at the bunker as they try to figure out why Black Siren has aligned herself with Cayden.
Felicity goes to see Alena to tell her that Cayden's plan was stopped. Alena suggests to Felicity to mass-produce the implant spine-chip for her and Curtis' start-up company. They agree to call it Helix Dynamics.
At an airport hanger, Cayden rewards Black Siren with a piece of technology. It will prevent Team Arrow from tracking her sonic powers. Cayden reveals how Felicity's takedown of the firewall actually worked in his favor.
Back at the apartment, Felicity and Oliver begin to make out before he gets a call. It's Slade Wilson who is asking Oliver for help.