Emerald, a gem with extraordinary powers, has broken out of the homeworld gems' ship and crash landed on Earth. With hints about who the Crystal Gems were, only with word from Homeworld, she meets them face to face.
Purple Sapphire is different, instead of seeing the future, she can make one.
After an outburst of rage, Purple Sapphire give Pink Diamond a fate of shattering, and she is wanted on Homeworld. Purple Diamond leaves homeworld and goes to a planet called Earth.
Since the Crystal Gems don't want her, she goes with the Shimmers... who are a a pack of gems.