As discussed here ‘The Time Of The Doctor’ reveals that the events of ‘The Pandorica Opens/The Big Bang’. The explosion of the TARDIS echoes through time, setting up a situation in which the other races realise that the Doctor is responsible and place him the Pandorica.
At the end of ‘The Pandorica Opens’ the Alliance reveal they used the memories of Amy Pond to build a trap for the Doctor, a scenario that he would believe. The two main elements are the story of Pandora’s box and her love of Romans.
River Song finds scorch marks (presumably of Daleks) at Amy’s house on 26th of June 2010, the day after the Doctor and Amy began travelling together. This indicates that in the day they were away the members of the Alliance arrived, found these elements and based their plan around it.
We don’t know why they needed to act at this particular period but since their plan hinged on using Amy’s memories that I had to wait until she began travelling with the Doctor. If it had been a different companion they would have waited until just after they had left with the Doctor instead.
The Alliance build the Pandorica and place it in the Underhenge. River says that it has been there for thousands of years. The Doctor is only able to find it because as it begins to open it uses Stone Henge as a transmitter broadcasting a signal that it is opening. This is picked up by Vincent Van Gogh who paints a picture containing co-ordinates that eventually end up in River Song’s possession.
Why does it choose this particular moment to open? The Daleks say that the Pandorica is ready because it has scanned the Doctor, allowing his limits and capacities have been extrapolated. We don’t know if this entire process has happened in the short time that the Doctor has been in the Underhenge or if it has been thinking about some of the problem for all these centuries.
It could be that it was always designed to open at this particular time period to make use of the Roman army. The Pandorica was allowed to age centuries to make it seem more authentic.
The Alliance needed the Doctor to be lured to the Pandorica, which requires us to think about how involved they were in Vincent Van Gogh picking up the transmission. Did they know he was mildly psychic or did they have to implant this talent (which could have resulted in his problems)? If the Doctor didn’t have the connection with Van Gogh how else did they plan to get him involved?
It could be that they deliberately let the Pandorica become the fairy tale that the Doctor and River have heard of. They might have hoped that the Doctor’s curiosity would eventually led him to search for it.
Whoever is responsible for the fairy tale has a sense of humour as the dark, monstrous entity that is trapped within is ultimately the Doctor. It could be that they were also counting on the Doctor seeking out this monster, as he typically opposes such evil.
The entity is said to have been tricked into entering the Pandorica by a good wizard. River says she hates stories with good wizards as they usually turn out to be the Doctor. This isn’t the case here, as it is the Alliance that force him into the box.
If the fairy tale is wide-spread then were the Alliance already aware of it when they created the Pandorica or, as the creators of this change in time, where they unaware of it until they actually made it?
The Pandorica has layers of security, including deadlocks, time stops and matter lines. You couldn’t die as the prison would keep you alive, for all eternity. Since the Alliance were trying to prevent the TARDIS from exploding and they mistakenly believed that he was the only one who could fly it why didn’t they kill him? Why did they put him something that would actually keep him alive?
It could be that the Alliance were aware that he was supposed to die at lake Silencio on the 22nd of April 2011. Their plan would require him to survive to this point, at which stage they could release him and he’d die, protecting time and not giving him a chance for the TARDIS to explode (hence why the future Doctor didn’t have it with him at the lake).
It could also be a form of insurance for the Alliance. Individual races might not have trusted other members and know that the Doctor might be the only way to save them from betrayal. Keeping him alive meant the members of the Alliance had a last resort if things went bad. In case of emergency break open the box for the Doctor.
The Pandorica was always designed to keep the Doctor in, rather than others out. At least one Cyberman was left to guard it and the Doctor guesses that it was decapitated and disarmed by Celts. Was there a risk that another person would open the Pandorica prematurely? If so it wouldn’t have mattered until the Doctor was placed in it so why have a guard?
Upon entering the chamber of the Pandorica River Song picks up fry particles everywhere, indicating energy weapons having been discharged on the site. The Cyberman is equipped with an energy weapon but is that enough for the particles to be everywhere? Could there have been larger battle here?
Due to their miscalculation the TARDIS still exploded. Countless worlds were wiped out, leaving the members of the Alliance as fossils, an afterimage of the erased species. Earth was at the eye of the storm and thus their extinction was delayed. We can take it that the Pandorica is responsible for protecting the Doctor.
What would the Alliance have done if this didn’t happen? Would they have left him in Underhenge or would they transport him somewhere else? Leaving him on Earth doesn’t seem particularly safe since he has so many allies there and there would always be the danger a past incarnation might stumble across him.
If they took him elsewhere would it be a neutral world or one owned by a member of the Alliance? Would the Alliance have stayed together or quickly broken down? How long before someone wanted to free the Doctor to save them?
With the universe rebooted how much of these events do the other races remember? Especially after the events of ‘The Time Of The Doctor’. During that long siege did they realise that the events of the Pandorica were a consequence of what happened at Trenzalore?
If this is a change in time then might the legend of the Pandorica been a corruption of what originally happened? It might really have contained a terrible blood-soaked being and the Doctor might actually have been the good wizard that trapped it inside (certainly there are shades of Fenric to this tale).
If the rebooted universe removes the events of the Alliance then this original chain of events might have occurred or will now occur with the 12th (or future) Doctor.
PCs can explore these events, the ramifications of the Alliances actions and discover future details of their plans within your own campaign. With time being rewritten multiple times there are plenty of versions of events to unravel.