10 Reasons Why The New Doctor May Actually Be River Song

Likewise, in both 'Fugitive of the Judoon' and 'The Family of Blood', the Doctor has a keeper - someone who knows their true identity and takes care of it for them. Both Lee and Martha Jones act as similar agents in this way.

While Martha protected the Doctor's pocket watch, Lee protected the fire alarm at the lighthouse. Both characters are key to giving the Doctor the ability to break the Chameleon Circuit - "Follow the light. Break the glass".

This comparison of episodes can also be seen through the "calling-out" of their hidden identities. While Tenant's Doctor could hear the pocket-watch whispering to him, Martin's Doctor could see visions of the lighthouse and fire alarm. In this, the TARDIS was guiding them both back to an identity.

However, Martin may not be truly out of the circuit; just as the TARDIS is stuck as the Police Box, River is stuck as the Doctor. Unfortunately, we did not spend any alone time with Martin's Doctor and therefore cannot determine whether she has another hidden object, keeper, or identity calling out to her.

But, as the Doctor says, "I believe there is more than one identity within you".