- "Any preference on how you'd like to die? The flame or the frost?"
- —Leonard Snart threatens The Flash
Leonard Snart AKA Captain Cold returns to Central City with the Cold Gun and a new hotheaded partner in town – Mick Rory AKA Heat Wave. The duo plan to steal a multimillion-dollar painting, but Cold has another agenda while in town – to set a trap for The Flash. Snart and Mick kidnap someone close to The Flash and threaten to kill them unless The Flash shows up for a battle of fire and ice. Barry tells Joe he isn’t sure he should take on Snart again after the casualties that happened the last time they fought. Meanwhile, Barry asks Dr. Wells, Caitlin and Cisco to help him double his training efforts so he's ready for the Reverse-Flash when the man in yellow returns to Central City. Iris deals with the aftermath of Barry’s confession, and Cisco makes the CCPD a new shield.
Barry discovers his plan, and agrees with Dr. Wells to not engage Snart in the hope that he goes away and no one gets hurt like the last time.
When the Flash fails to show, Snart and Rory, who now has a gun that can emit absolute hot temperatures, kidnap Caitlin to force Barry out of hiding. Captain Cold freezes Caitlin's car closed when they kidnap her.
Cisco and Barry realize that if they can get Snart and Rory to cross the streams of their respective weapons it will cancel the two guns out. Snart and Rory challenge The Flash to meet them for a battle of fire and ice in the city and to show the world he's real or they'd kill Caitlin. After multiple failed attempts, Barry eventually gets them to cross the streams with Eddie's help, successfully damaging the weapons and disabling the criminal pair. While in transport to Iron Heights Prison, Snart and Rory are broken out by Snart's sister. Meanwhile, Caitlin investigates the cause of Ronnie's transformation before being kidnapped.
- During the training session, when Barry appears to be stunned, Dr. Wells tentatively puts out his left foot as if rising from his wheelchair, then relaxes when it's clear Barry is OK.
- When preparing for Barry's rematch with Snart and Rory, Cisco and Barry compare the plan to disable their weapons by tricking them into firing at each other to the concept of "crossing the streams" from the film Ghostbusters, with Cisco noting that the film was surprisingly scientifically accurate.
- When opening up his 'Nerd Survival Pack' that Iris found, one of the comic books Barry pulls out is "Space Ghost".
- It appears the feedback from the heat and cold guns affected Mick and Snart's vocal cords. When they return, Mick sounds gruffer and Snart sounds more nasally.
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