- "I promised there wasn't a single case I couldn't crack. And a promise made is a promise kept. Dibny detects."
- —Ralph Dibny
Cisco is shocked when Gypsy's father, Breacher, shows up on Earth-1. Breacher takes an immediate disliking to Cisco and decides to hunt him. Meanwhile, Barry runs into his old nemesis, Ralph Dibny.
Gypsy's father, Breacher, attacks Cisco, vowing to hunt and kill him in 24 hours, allowing the romance should he survive. Team Flash learns that the bus driver was murdered and tracks down another passenger, Ralph Dibny, former corrupt CCPD detective exposed by Barry and currently an infamous private investigator.
As two thugs attack Dibny, he is revealed to have the power to stretch. Caitlin stabilizes his powers with a serum. The team learns that Ralph has been blackmailing Mayor Bellows for adultery, with the latter revealed to have hired the thugs. Barry confronts Ralph for his actions while the latter scolds him, claiming to have been a "good cop".
He later stops blackmailing Bellows, who still attempts to kill him while Breacher mistakes the former for a Plastoid, the species that invaded Earth-19 previously, and attacks him. Cisco intervenes and saves Ralph, whom Barry, having revealed his alter-ego, convinces to help arrest an escaping Bellows.
Admiring Cisco's gallantry, Breacher allows the relationship. Gypsy and Breacher then return to Earth-19, to stop a potential breacher.
Barry recruits Ralph for Team Flash and learns that someone named DeVoe instructed Ralph to watch Bellows. Barry remembers that Abra Kadabra and Savitar both mentioned DeVoe.
Meanwhile, Caitlin finds a message from Blacksmith on her apartment door; "We Miss You. Come Back Song".
- This is the second episode that Tom Cavanagh has directed.
- The title of this episode is possibly a play on the name of the 1962 film Long Day's Journey into Night.
- This is the first episode of the series to not feature Neil Sandilands (Clifford DeVoe) after signing on as a series regular.
- Cisco claims that Breacher literally killed someone with his face. This is likely a reference to Danny Trejo's role in the TV series Breaking Bad, in which his character Tortuga's head is severed from its body, then later explodes to kill a DEA agent.
- Cisco refers to Breacher as "the Predator" and himself as "the Schwarzenegger", referencing Arnold Schwarzenegger's role in the 1987 film Predator.
- Cisco pulls out a Machete as one of the weapons to use against Breacher which Harry advises against. This is a reference to Danny Trejo's role as Isador "Machete" Cortez in the Spy Kids franchise.
- Ralph Dibny claims to look like "a Hemsworth", referencing actors Chris and Liam Hemsworth, who are known for their muscular appearances.
- A poster for the 1999 film The Matrix can be seen on Cisco's bedroom wall, before Breacher destroys it.
- The IOU card Ralph left is dated October 10, 2017, which Barry claims is the same day he came out of the Speed Force in "", however since "" takes place on May 24, 2017, and "The Flash Reborn" takes place 6 months after the events of "Finish Line", that would place the events of "The Flash Reborn" sometime around November 24, 2017.
- When Barry and Iris are investigating Ralph Dibny's office, Iris opens a drawer and a bottle of Gingold is shown to be inside the drawer. In the comics, "Gingold" is the drink that gives Dibny his elastic powers.
- Ralph Dibny was previously mentioned as a victim of the particle accelerator explosion at S.T.A.R. Labs. However, due to Flashpoint, his fate was changed.
- Bellows mentions that before he was the mayor, he was a police officer. This is most likely referencing that Vito D'Ambrosio, who also played Anthony Bellows (Earth-90) from the 1990 series, in which he was a police officer.
- Barry suggests Ralph the nickname "Plastic Man", a reference to the DC hero with similar powers to Ralph.
- The scene where Barry fights the mayor's henchmen is similar to how Quicksilver fights the Pentagon's guards in the 2014 film X-Men: Days of Future Past.
- When Cisco is leaving the lab to take Breacher to coffee, Harry tells him to "Have fun storming the castle." This is a quote from Billy Crystal's character, Miracle Max, in The Princess Bride.
- Ralph Dibny's client is called "Mrs. Broome". This is a reference to John Broome, the comics writer who created the Elongated Man.
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