"All for Nothing" begins with Oliver meeting with Lance, Dinah, and the newly appointed Captain Hill. Hill briefs the group that Cayden James is monitoring all traffic entering and exiting the city.
We see an ARGUS agent surface from the lake standing by, asking for orders from Oliver. When Oliver orders them to go get James, the ARGUS agents in the water are electrocuted.
Back at his office, Oliver wires $70 million to James.
We see a news report saying that Cayden James has had a stranglehold on the city for eight days and supplies are starting to get low.
Vincent approaches Dinah asking if she trusts him or not. She kisses him.
In a flashback, we see Captain Singh introducing Vincent and Dinah on their first day at the Central City Police Department.
Vincent is seen meeting with Richard Dragon, the Bratva, and Cayden James at one of James' hideouts. There, Cayden reveals that he doesn't like surprises and hints that he knows that Vincent is a traitor.
Oliver and Felicity are talking at Arrow HQ. She reminds him that once Cayden James is put away, she's looking forward to going on their honeymoon. An alert starts going off — Felicity's tracker is going off.
Oliver and Diggle converge on the location of the tracker and find Vincent. As Oliver's getting ready to shoot him, Curtis and Rene run out and inform Oliver and Diggle that Vincent is undercover with Cayden James.
The two splinters of Team Arrow meet with Vincent about Cayden's plans. He reveals that if Oliver enters Cayden's hideout, he'll detonate the thermobaric warhead, leveling most of Star City. After hearing more about Cayden's plan, Felicity and Curtis determine that Vincent will need to go deeper undercover to place a special device on a server that will allow Team Arrow to disable Cayden's weaponry.
At Lance's office, he tells Thea that he's caught the Earth-2 Laurel following him as of recent, but whenever he goes to turn around and confront her, she disappears.
Dinah pulls Vincent aside and asks if Oliver's the one that put him up to do the mission, and Vincent says he's doing it on his own accord.
We see another flashback where Vincent and Dinah are still undercover.
Curtis, Rene, and Dinah return to the original Arrow HQ. They've gathered to track Vince's progress. He's able to get into the server room and once he starts transferring the files, Cayden walks in and catches him.
Cayden approaches him, and through the Team Arrow comm systems, Felicity gives him a few lines to say about IT so he doesn't blow his cover. He's able to distract Cayden long enough for the file transfer to complete.
Vincent is able to get outside of James' compound and transmits the files he took off the server back to Felicity and Team Arrow.
Cayden follows Vincent outside where he calls the latter a traitor and stuns him with a stun gun.
At Arrow HQ, Dinah's getting worried that she hasn't heard from Vince in a while. She decides to go to Helix, and Rene decides to go with.
Cayden's questioning Vincent, where he finds out Vincent is a metahuman with regenerative capabilities. Cayden and Dragon leave Vincent alone with Anatoly to get tortured.
Thea's helping Lance keep an eye on Laurel. He tricks her and is able to lure her to a place with multiple pictures of the Earth-1 Laurel. She gets upset and destroys the screens showing the pictures.
Felicity tracks the location of the bomb when they finally locate
The trio converges on Vincent's location and
Oliver and Diggle go to the warehouse where the bomb is located and find that the warehouse is empty, and instead, Cayden and his crew have strapped a handful of civilians with explosives set to detonate in a few minutes.
Dinah finds Vincent, and they're soon rattled by an explosion. They regain consciousness, and Dinah is trapped under rubble. Vincent goes to help her when he's blown away by Black Siren. He's impaled on some rebar sticking out of the wall. Black Siren approaches Vincent and uses her powers point-blank, killing him.
Curtis and Rene rush in and rescue Dinah.
Dinah's back at Helix HQ mourning the loss of Vincent. Curtis and Rene inform her that Oliver and Diggle were unable to locate the bomb, upsetting Dinah even more as she thinks Vincent died for nothing.
Oliver and Diggle return to Arrow HQ and find out Vincent
Lance is back at his office looking through scrapbooks when Thea walks in and tells him they may have been wrong about the Earth-2 Laurel turning good. She tells Lance that she's the one that killed Vincent.
Oliver goes over to Dinah's to talk to her about the events earlier that night. Oliver tries calming her down, but she pledges on killing every last one of Cayden's people -- starting with Laurel.