Cup of Athelstan
From Tardis Wiki, the free Doctor Who reference
The Cup of Athelstan was a historical treasure stored in the International Gallery in London. It was given to Athelstan, King of England, in 924 AD as a coronation gift from Hywel, King of the Welsh. It was worth 18 million pounds. Lady Christina de Souza stole it in Easter 2009 and then travelled on a double-decker bus through a wormhole to another planet. The Doctor later used it to get the bus and the passengers onboard back through the wormhole to Earth; unfortunately he had to destroy the cup in the process. (DW: Planet of the Dead) The Cup was referenced in The Mona Lisa's Revenge
After The Cup of Athelstan's disappearance, security was improved for the Mona Lisa.
