Crescent Moonbeam is a recent release from Canterlot Mental Asylum, recovering from a severe case of schizophrenia, she's looking for a place for a fresh start. She moves to Ponyville and asks Twilight if she can stay for a little while as she sets up in Ponyville. This is the first story.
...That's where what starts?
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Mostly this is just the start of her adventures that she will have later. This first bit is setting everything up. Other adventures will be coming soon.