This second "Special", following the events of Doctor Who's fourth season with companion Donna Noble, has The Doctor on his own in present day London. He boards a double-decker bus in search of a spacial rift--and the vehicle, along with the passengers, is transported to another planet. Also on board is Lady Christina (Michelle Ryan), who has just stolen a multi-million dollar gold artifact from a museum.
One of the humans on board is a low-level psychic whose abilities have been magnified--and she insists that "death" is coming for them. Christina appoints herself a the groups leader and she and the Doctor go out exploring the desert landscape. They come across a fly-like alien and are taken to his spaceship, which had crashed. They discover that this world was populated by billions of beings a year before but that something turned them--and their cities and all other life--into grains of sand. The creatures responsible are these stingray-like beasts that devour planets. They are the ones who created the wormhole, as part of their natural life cycle--and soon Earth will be on the menu. The Doctor is able to communicate with UNIT on Earth and with the help of a crazy scientist manage to close the wormhole just in time.
This is an interesting story because it seems like Christina would be his ideal companion, but he refuses to take her along on his adventures. The tale also hits that the Doctor will face death soon, which culminates for this version of The Doctor in THE END OF TIME...