Barry cannot keep resetting time until it is perfect; he must learn to live with the consequences and the "cracks" he created in his own reality. 💔 The Timeline "Cracks" (The Fallout)

Introduced as Barry's new, arrogant CSI lab partner (played by Tom Felton). He has worked with Barry for a year in this rewritten timeline, and he openly distrusts him.

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Sullen and not speaking to each other because Joe kept the secret that Iris's mother was actually alive.

When Barry returns to what he thinks is his normal timeline, he realizes his relationships are shattered:

The central metaphor of the episode is delivered by Earth-2's Flash, Jay Garrick. He pulls Barry out of the Speed Force and uses a coffee cup to explain time travel:

If you break a coffee cup and glue it back together, it might hold water again, but it will always have cracks.