The Family of Blood

The Family of Blood, in the form of the humans they have possessed, hold Martha and Joan Redfern captive at the village dance; demanding that John Smith—the Doctor's human form—make a choice about which of the two to save. As John tries to decide, Timothy Latimer, in possession of the Doctor's fob watch containing the Time Lord persona, briefly opens it up again (terrifying the Sister with an image of the Doctor at his most cruel and merciless), which is detected by the Family and momentarily distracts them, allowing John, Joan, Martha, and the other villagers to escape, collecting at the school. John helps to organise the school's defenses while Martha and Joan search for the fob watch.
The Family assault the school with an army of scarecrows, but the boys in the school are able to defend the first wave. When the Family attempts to show John that they have discovered his TARDIS, Joan, having seen the images of the TARDIS in John's "Journal of Impossible Things", realises that John is really the Doctor. As the Family continues to assault the school, John, Joan and Martha escape to the cottage of the little girl's family which the Family had possessed. Realising that the Doctor has left the school, the Family returns to their ship and begins an aerial bombardment of the village. As John and the others take shelter, Tim arrives and returns the watch to John, and both Martha and Joan implore John to use it to become the Doctor and save everyone. John is hesitant as using the watch is the same as committing suicide. Joan takes John aside and shares a series of images generated by the watch showing what their lives may have been like in the future, happily settling down, raising a family, and growing old together. Joan admits that she would love that future, but that the Doctor is needed now.
On the Family's ship, John is let aboard, fumbling about the strange interior and surrendering the watch as to stop the bombardment. When the Family opens the watch, they find it empty and realise that John has changed himself back into the Doctor. The Doctor warns the family that his early bumbling has purposely caused the ship to go into overload, and they all escape before it explodes. The Doctor then punishes the Family for their destruction, giving each of them a form of twisted immortality, such as being stuck at the event horizon of a collapsing galaxy or being trapped in every mirror in existence, when all the Doctor was trying to do was let them die out peacefully. The Doctor returns to Joan, offering her travel aboard the TARDIS but she cannot accept as she loved John but cannot come to love who the Doctor is. The Doctor gives her his Journal as she leaves. The Doctor and Martha say their goodbyes to Timothy, letting him keep the empty fob watch for himself.
A year later, as Timothy aids Hutchinson in World War I, his visions from opening the watch are able to save the two from being hit by a shell, and both survive the war. In Timothy's old age, he participates in Remembrance Sunday, and spots the Doctor and Martha from afar, both wearing artificial poppies. Timothy and the Doctor silently acknowledge each other as the service continues.