Summary: The Doctor can't do anything to help earth right now, but there's one person who can.
The fate of the earth and all of humanity was in the balance, and under normal circumstances the Doctor would have been there to fix whatever was wrong, ensure the future would happen exactly as it was meant to. It was a task he’d set himself long ago, when his fascination with the planet and its people had first begun.
But this time he was trapped, a wizened creature locked in a cage, every year of his centuries-long existence visited upon a body that should still be young. The Master’s doing.
All his hopes now rested on Martha Jones’ shoulders.