Doctor Who Multi-Doctor RPG: The 9th, 10th, 11th, and 12th Doctors meet up in some way(Yet to be determined, 9th could be before he met Rose, 10th could be during his Regeneration specials, 11th could be during Trenzalore, etc.), and discover a fiendish scheme by either the Master or the Daleks(Or both!

) to end the world in some sinister manner(as if you could end the world in a non-sinister manner). The four Doctors and the appropriate companions(Pretty much Clara, though the points in the Doctor's timeline could be altered in order to accommodate more companions) then set off to stop this evil scheme with TARDISes, Sonic Screwdrivers, and incredible intellect.
I'll work out the rules upon winning(Because I will obviously win >=] *promptly begins bribing people with pennies*)