Here is the synopsis for The Unicorn and the Wasp
'In 1926, Agatha Christie disappeared for 10 days. Was it amnesia? A nervous breakdown? Or a Giant Alien Wasp? As Russell T Davies's BAFTA award-winning time-travelling drama continues, the Doctor and Donna join forces with the world's most famous crime novelist to encounter a body in the library, poisoned cocktails and a Vespiform seeking revenge.
In other news you can find various Doctor Who Magazine pictures from upcoming episodes here