Many stars of Doctor Who come together on this anniversary special.

Clara is working as a school teacher.

A gigantic claw picks up the Tardis, it's Kate Stewart taking it to help with a special case, from Elizabeth 1.

The Doctor sees a painting that Elizabeth I sent to let The Doctor know she was who she said, and it sends him back to remembering the time when he destroyed his Gallifrey and all the people on it during the war against the Daleks, when he was the Warrior Doctor.

The Warrior Doctor is visited by the image of Rose Tyler as the interface or the conscience of the moment caused by the most dangerous weapon in the universe (the one that will destroy Gallifrey). Except she is the the Bad Wolf in this incarnation. 

Bad Wolf tells Warrior Doctor that his punishment for burning all of the children of Gallifrey will be to live, and she wants to give him a glimpse to the man he will become based upon the action he will take.

The Doctor and Clara walk into a room showcasing a painting of Elizabeth I and the 10th Doctor.

The 10th Doctor is wooing Elizabeth I who he thought was a Zygon, but the Zygon was actually his horse, so he inadvertently asked the virgin queen to marry him. Then there were two Elizabeths, a time portal opened a fez dropped through and then so did The Doctor.

The 10th and 11th Doctors come face to face.

The Elizabeths run to safety and then the Doctors talk to Clara through the time portal. The Fez didn't go through to Clara, but to the Warrior Doctor, who then comes through the portal, fez in hand.

The three Doctors fiddle about and get themselves incarcerated in the Tower of London because that's where Kate Stewart's office is located.

Osgood realizes why the statues were smashed.

Clara and Kate go to the Black Archive to see a time travel device bequeathed to them by Jack Harkness upon one of his deaths. Clara had been there before, but her memory was wiped, as are all who enter.

The three Doctors try to use their collective screwdrivers to free themselves from the Tower.

The Warrior Doctor doesn't realize how much the decision he has yet to make affected the two Doctors before him. Rose, Bad Wolf, urges him to as what he needs to know.

Warrior Doctor doesn't recognize who he will become if he makes the decision to destroy Gallifrey to save the universe.

Elizabeth I ensures The 10th Doctor keeps his promise to marry her. 

Kate Stewart puts London in the same place that Gallifrey was in when the Warrior Doctor destroyed it. The Doctors try to tell her to stand down.

Clara rescues The Doctors from the Tower and the stop Kate and Zygon Kate from destroying London.

Clara talks to the Warrior Doctor, telling him his eyes are younger looking than her Doctor's and he makes his decision.

Warrior Doctor stands before a big red button and Rose/Bad Wolf asks if he is sure.

Rose tells Warrior Doctor that the wheezing, groaning sound of the TARDIS brings hope to anyone who hears it, even him.

The 10th and 11th Doctors arrive to help Warrior Doctor with his decision.

Clara reminds The Doctors who they are and why they don't need to make the decision they think is a given. They decide to freeze Gallifrey for a moment in time and let the Daleks destroy themselves.

All 12, no 13 Doctors work together to save their home.

Warrior Doctor doesn't know if they succeeded, nor did the 11th Doctor.

Warrior Doctor gets into his TARDIS and regenerates.

The Doctor learns the true name of the painting is Gallifrey Falls No More, because they succeeded in saving their home. The Curator tells him, and the curator is the 4th Doctor.