- "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.|
- Grant Gustin as Barry Allen/The Flash
- Candice Patton as Iris West
- Danielle Panabaker as Dr. Caitlin Snow
- Carlos Valdes as Cisco Ramon/Vibe
- Tom Cavanagh as Dr. Harry Wells
- Jesse L. Martin as Detective Joe West
- Hartley Sawyer as Ralph Dibny
- Jessica Camacho as Cynthia/Gypsy
- Vito D'Ambrosio as Anthony Bellows
- Danny Trejo as Josh/Breacher
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 Soon".
- 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 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.
- When Barry and Iris are investigating Ralph's office, Iris opens a drawer and finds a bottle of Gingold inside. In the comics, "Gingold" is the drink that gives Ralph Dibny his elastic powers.
- Ralph was previously mentioned as a victim of the S.T.A.R. Labs particle accelerator explosion in Season 1's "". However, due to Flashpoint, his fate was changed.
- Anthony Bellows mentions that he was a police officer before becoming mayor. This is a reference to Vito D'Ambrosio also portraying Anthony Bellows in the 1990 series, in which he was a police officer.
- Barry suggests the nickname "Plastic Man" for Ralph, a reference to the DC hero with similar powers to Elongated Man.
- 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 out for 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's client is named "Mrs. Broome". This is a reference to John Broome, the comics writer who created the Elongated Man.
- Ralph wiggles the tip of his nose in the final scene and says, "I smell a mystery!" These are two things he was known to do often in DC Comics as Elongated Man.
- Upon seeing Harry, Breacher says his daughter Gypsy was sent to hunt someone who looked like him, referencing Gypsy's first appearance where she was sent to capture Harry's doppelgänger, H.R. Wells.
- The "I.O.U." 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 "" took place on May 24, 2017, and "" 6 months later, that would place the events of the season premiere sometime around November 24, 2017.
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