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The Flash -- "Flash Back" -- Image: FLA217a_0055b.jpg -- Pictured: Jesse L. Martin as Detective Joe West -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217a_0086b.jpg -- Pictured: Grant Gustin as Barry Allen -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217a_0105b.jpg -- Pictured: Grant Gustin as Barry Allen -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217a_0119b.jpg -- Pictured: Rick Cosnett as Detective Eddie Thawne -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0009b.jpg -- Pictured: Carlos Valdes as Cisco Ramon -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0049b.jpg -- Pictured (L-R): Carlos Valdes as Cisco Ramon and Andrew Mientus as Hartley Rathaway -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0058b.jpg -- Pictured (L-R): Carlos Valdes as Cisco Ramon and Andrew Mientus as Hartley Rathaway -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0178b.jpg -- Pictured (L-R): Danielle Panabaker as Caitlin Snow, Carlos Valdes as Cisco Ramon and Andrew Mientus as Hartley Rathaway -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0300b.jpg -- Pictured: Grant Gustin as The Flash -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0307b.jpg -- Pictured (L-R) Tom Cavanagh as Harrison Wells and Grant Gustin as The Flash -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0308b.jpg -- Pictured: Grant Gustin as The Flash -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.

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The Flash -- "Flash Back" -- Image: FLA217b_0380b.jpg -- Pictured: Grant Gustin as The Flash -- Photo: Diyah Pera/The CW -- © 2016 The CW Network, LLC. All rights reserved.