Doctor Who: Imagination

The noise interrupts her music, and while at first confused, Sarah soon realises what it is.
She might not have been with the Doctor and the Ponds long, but she soon discovers a shocking secret that changes her life forever.
And... is it just her, or does the Doctor seem... off?
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COMPLETE - First of Sarah's adventures with the Doctor.
1 - Imagination
2 - New Visitor
3 - The Impossible Angel
4 - The Wrath of Demonns