With only two episodes left in "The Flash" Season 3, Barry and his team must do everything they can to stop Savitar from killing Iris. During "Cause and Effect," tonight's episode, Tracy Brand successfully created a Speed Force trap for Savitar -- but now she needs a power source more powerful than the sun to fuel it, and Barry knows just the thing.

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In "Infantino Street," the penultimate episode, Barry will need to recruit Captain Cold to steal an alien power source that's being held at A.R.G.U.S. Unfortunately, A.R.G.U.S. guards will be the least of Barry and Snart's worries. As you can see in this episode promo below, the power source is guarded by none other than King Shark, the mutated shark with extraordinary strength.

Per the episode description,

THE COUNTDOWN BEGINS; WENTWORTH MILLER RETURNS AS CAPTAIN COLD – With only 24 hours left until Savitar murders Iris (Candice Patton), Barry (Grant Gustin) struggles to save the woman he loves and makes the choice to use any means necessary to do so. Realizing he has one option left to save her, The Flash turns to Captain Cold (Wentworth Miller) for help. Michael Allowitz directed the episode with story by Andrew Kreisberg and teleplay by Grainne Godfree. Original airdate 5/16/2017.

Starring Grant Gustin as the Scarlet Speedster, “The Flash” airs Tuesdays at 8 pm ET/PT on The CW. The series also stars Jesse L. Martin, Tom Cavanagh, Carlos Valdes, Candice Patton, Danielle Panabaker, Keiynan Lonsdale and more.