In some ways it's hard to believe that The Flash is coming up on its 100th episode, but the timing is pretty perfect. "What's Past Is Prologue" will serve as the show's midseason finale, airing before the "Elseworlds" crossover (so that event can just totally be its own thing). Arrow had the challenge of its 100th episode being in the middle of a crossover, but still owned that hour by investigating its past in a really thoughtful way. The Flash is planning something similar without that extra crossover burden, in an episode directed by Tom Cavanagh and written by Todd Helbing and Lauren Certo:

In the 100th episode, Barry (Grant Gustin) and Team Flash come up with a plan to stop Cicada (Chris Klein).  However, the plan calls for Barry and Nora (Jessica Parker Kennedy) to travel back in time to gather some key necessities. However, Barry hesitates, concerned about his daughter seeing certain parts of his life.  Meanwhile, Sherloque (Tom Cavanagh) takes his concerns about Nora to Iris (Candice Patton), and Caitlin (Danielle Panabaker) turns up a key asset in the fight against Cicada.

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Image via The CW

According to TV Line, we also know that Zoom will be one of the blasts from the past that Barry will encounter, and "is but one of several fleet-footed foes to appear in the milestone episode, and that they’re all 'wanting a piece of Barry.'"

Seeing The Flash's greatest hits will be fun, although it could make us a little too nostalgic for the show's truly better times. Having said that, The Flash's fifth season is actually finding that promised balanced a lot more than I was expecting it to (after we've been promised tonal course-corrections for the last several seasons). It's quirky and it's fun, but it's also still action-packed and, most crucially, it's finding plenty for its non-Barry characters to do -- especially Iris (in probably the best arc she's had maybe ever).

But ... what is up with Sherloque's concerns about Nora?

"What's Past Is Prologue" will air Tuesday, December 4th on The CW.

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Image via The CW
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Image via The CW
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Image via The CW