The Doctor started running around to random people, asking them if anything abnormal has been happening with their shadows. Most replied in the negative, but some of them didn't. The Doctor heard stories varying from shadows moving without the host person moving, shadows disappearing when everyone else had shadows, Isabella's Case, or feeling like people were being watched, when they were alone. Alone with their shadow.
When the Doctor gathered enough evidence that yes indeed something strange was going on, he urged Isabella into the TARDIS. She wasn't as surprised about the "bigger on the inside" space-time machine, but the Doctor figured it was either that she was young and her brain was still a soft pudding mix, or that she was too scared to care. When he walked inside, he ran through the Galactic News on the monitor. He got 3 total intergalactic crises relating to shadows.
The Doctor had two enemies that they could be dealing with. One was the Vashta Nerada, but he ruled them out when everyone had only one shadow. The Vashta Nerada always gave the host two shadows. His second thought was that they were fighting an ancient warrior race, the Shadowmen. According to the old Gallifreyan legend, the Shadowmen were an old race who lived as shadows. When they found a host, they were free. Most of them were peaceful and just followed the actions of the host. But the others, the warriors, didn't. The warriors were born different than the other Shadowmen. The warriors could become human.
But the Doctor had almost ruled them out because they were old. Older than even some of Gallifrey. But the thought was always in the back of his head. He glanced over at Isabella, and caught the shadow waving at him.
It has to be the Shadowmen. The Doctor was fighting with himself. What other race would dare interfere with the shadows of living beings?
Isabella asked if she could call her grandmother and the Doctor replied with "Of course."
He handed her the phone. She rang up her grandmother.
"Hello?" A voice called. The Doctor recognized this voice, but he couldn't get at it.
"Grandma? It's me, Isabella." She replied in a soft tone. "I'm with a man named the Doctor. I'm scared."
"The Doctor, eh? Can I talk to him?"
Isabella nodded and handed the phone to the Doctor. He laughed when Isabella nodded.
"Hello? I'm the Doctor." He said.
"Doctor, this is a voice I haven't heard in a long, long time." Isabella's grandmother said.
"I'm sorry, do I know you?"
"Doctor, it's Me."
"Am I supposed to know who you are?"
"I just told you. It's Me."
It hit the Doctor. "You're Me? You have a grandchild?"
"I have hundreds."
"So that's why she wasn't surprised when she saw the TARDIS. You tell her the stories. Tell me Ashildr, what to you know of the Shadowmen?"
"Ashildr?"
"That's you. Before you became Me. I keep telling you that. The last time I told you was when Clara... had her accident."
"You call it an accident?"
"You call it beautiful?"
There was a long pause before anyone spoke. Me broke the silence.
"Where are you Doctor? I'll meet with you."