Ricardo Diaz has kidnapped Roy Harper in an attempt to coerce him to testify against Oliver. Thea puts the Speedy suit back on to rescue him. Meanwhile Team Arrow has to deal with ramifications of Black Siren's gambit to to impersonate her Earth-1 counterpart.
- Actor Allusion: SCPD found a stuffed polar bear among Cayden's belongings.
- Artistic License – Law: Oliver's lawyer tries to get his case dismissed (see Hope Spot below) based on the fact that the DA got Renee to testify against him using evidence of Renee's vigilantism, which Cayden James got illegally. However, the "fruit of the poisonous tree" principle which Oliver's lawyer cites only applies to evidence obtained by the police in violation of the Constitution. Since James is a private citizen, it would only apply if the police told him to get the evidence.
- Even if the principle did apply, all it would do is make Renee's testimony inadmissible in court. The case itself wouldn't be dismissed just because the prosecution can't introduce some of its evidence.
- Air Vent Infiltration: Cited by Thea as to why she has to suit up again to rescue Roy, as she's the only one who's small enough to do this.
- Arbitrary Skepticism: Averted. "Laurel's return" is not met with skepticism because the Arrowverse has seen more than its share of weird things by now.
- Antagonist Title: "Doppelganger" is used for Alternate Selves in the Arrowverse, and Black Siren is the alive counterpart of Earth-1 Laurel.
- Badass in Distress: Roy has been kidnapped by Diaz.
- Bait the Dog: Once again, the episode teases the chance of redeeming Black Siren very hard...only for the reveal of her being a mole for Diaz.
- Benevolent Boss: As long as they don't betray him, Diaz seems to actually treat his men quite well, referring to them as brothers or family.
- Big Damn Kiss: Thea to Roy after rescuing him, then she quickly backs off thinking he must be be involved with someone else by now. He admits that he didn't take her advice about getting the family and the minivan (anyway, he hates minivans).
- Blackmail: Black Siren makes it clear that she could testify against Oliver if he spills the beans about her true identity.
- The Bus Came Back: Roy Harper returns to Star City, having not been seen since Season Four. The doctor who treated the late Earth-1 Laurel during her death also makes a comeback.
- Bittersweet Ending: Roy is rescued, but Diaz is still in control of the city. Also, Anatoly is in custody, but since the DA and the cops are on Diaz's payroll he'll likely be back on the streets soon enough.
- Cerebus Call-Back: The media coverage of Black Siren's "return as Laurel" is very reminiscent of Oliver's return from Lian Yu in the series premiere. Oliver and "Laurel"'s conversation at the late Earth-1 Laurel's apartment door is also reminiscent of their usual conversations in the first two seasons.
- Corrupt Cop: Half the SCPD force is under Diaz's payroll.
- Crocodile Tears: Black Siren, in front of the press.
- Dead Person Impersonation: Black Siren goes all the way, publicly announcing herself to be Earth-1 Laurel Lance.
- Double-Meaning Title: The title seems to only refer to Black Siren, but the episode also features the return of Roy, who took the identity of the Arrow to take all the blame from Oliver back when Ra's framed him. There's also the fact that Diggle, Oliver's go-to guy to dress as his vigilante identity everytime Oliver himself couldn't, expressing his desire to officially make himself the latter's Legacy Character.
- Enemy Mine: Oliver urges Dinah and Quentin to work together rooting out the corrupt cops at SCPD, because despite the bad blood between them, both are still upstanding cops. They do.
- Glad-to-Be-Alive Sex: Roy and Thea engage in some after the former is finally rescued.
- Honor Before Reason:
- Averted with Dinah. She's able to put her vendetta on hold when she finds out that Diaz has corrupted the SCPD.
- Played straight with Oliver, as he won't let Dinah on the mission to rescue Roy, since neither of them trusts the other. She's visibly hurt by this, hinting that she may be starting to wake up to the pain she's caused him.
- Hope Spot: Oliver's lawyer, Jean Loring, thinks she can get Watson's case against him dismissed, unaware the DA is secretly plotting to put him behind bars on Diaz's orders.
- How the Mighty Have Fallen: Oliver is disgusted that Anatoly has become just another thug for hire.
- Hypocrisy Nod: Oliver acknowledges that he shouldn't be the one lecturing Speedy on letting her emotions cloud her judgment (when it comes to Roy), but still insists he isn't wrong to point it out.
- Internal Reveal: Team Arrow, Quentin, and Dinah learn that Diaz was the one who killed Cayden, is the Big Bad pulling the strings in the underworld now, and has more or less bought out at least half of the police department.
- I Want My Beloved to Be Happy: Oliver tells Thea that even though he would miss her if she left, she should leave with Roy so she can find the same happiness he has with Felicity.
- The Kindnapper: A SWAT Team is charging towards the room where Thea is rescuing Roy but due to his wounds he can't escape. Thea turns to aim her bow at the door, only to be yanked backwards out the window by Oliver's Trick Arrow.
- Kingpin in His Gym: Diaz's first appearance in this episode has him sparring with a minion in his base, likely a Mythology Gag to how his namesake was posing as Richard Dragon.
- Meaningful Name: A doppelgänger is a being who is able to look like someone else, most commonly used in the Arrowverse for the case of an Alternate Self.
- The Mole: After Black Siren apparently proves herself by tipping off Team Arrow about where Roy and Diaz is, she receives a text from Diaz saying, GOOD WORK.
- Nerves of Steel: Diaz is quite collected throughout the entire encounter with Team Arrow, as he knows that they can't do anything to him due to having half the SCPD in his pocket.
- No Honor Among Thieves: Anatoly doesn't seem bothered by Cayden James' death at the hand of Diaz at all. Then again Cayden did lie about arranging an air lift out of the city before his bomb went off.
- Police Brutality: Diaz's crooked captain had some of her men illegally kidnap Roy and torture him in a hotel room to get him to agree to testify against Oliver.
- Pragmatic Villainy: Anatoly has aligned himself with Diaz despite knowing what he did to Cayden's son because he's only interested in getting revenge on Oliver and making money and as long as Diaz can make that possible, he has no complaints. That and Cayden left him to die.
- Properly Paranoid: For obvious reasons, Team Arrow is wary to trust Black Siren's intel on Diaz and Roy's location, suspecting a trap. They're right to be distrustful, for she is setting them up, but not in the way they expected — she's The Mole on Diaz's orders.
- Redemption Rejection: Though Black Siren claims she wants to act more like Earth-1 Laurel, it's all a lie; she's working for Diaz by the end of the episode.
- The Reveal: Diaz took Cayden's money.
- Series Continuity Error: Diaz works out from how Speedy has come out of retirement that there's a personal connection between her and Roy Harper, but he should know that anyway, given that they were dating at the time when Roy was arrested for being the Arrow.
- She's Back: Having been out of the suit for two years, Thea decides to become Speedy again to help Oliver save Roy.
- Sexy Discretion Shot: Roy and Thea are last shown kissing in the bed before the camera cuts to a spy of the League of Assassins.
- Suddenly Shouting: Diaz, who has been calm and collected throughout all of his appearances yet, loses his temper with Laurel due to her running off with the money before.
- Tempting Fate: Oliver, Thea and Quentin are saying they have to stop "Laurel" before she gets to the press, only to turn the corner and find her holding a press conference.
- Unexplained Recovery: Dinah talks to the doctor who pronounced Earth-1 Laurel's death. She admits it's hard to believe that she could be alive, but if a man can run faster than light, then what else is possible?
- We Can Rule Together: Diaz offers Roy a place in his organization.
- We Need a Distraction: Oliver fires an arrow that sets off fireworks to distract the police guarding Roy so Thea can zipline across to the building.
- Wham Line: The DA's new witness against Oliver? Roy Harper.
- Wham Shot: In the final scene, a member of the League of Assassins spies on Roy and Thea, and tells her master that she has found Ra's al Ghul's heir.
