The plot is promised as allowing the player to take on the role of the Doctor and River Song as they travel across space and time in an effort to save Earth by gathering pieces of the eternity clock, an object that is a record of everything that has or will ever happen in all of existence. Along the way is decision making which leads to "multiple possibilities" and puzzles. Players will encounter Daleks, Cybermen, Silurians and The Silence. The game had previously been confirmed for release on 30 April 2012, but was later postponed to 23 May 2012.
The game takes place just before the events of "Silence in the Library/Forest of the Dead" in River Song's timeline as indicated by various notes within her diary as well as the use of her title of 'Professor'. For the Doctor the game presumably takes place between series six and seven.
Source: Wikipedia, "Doctor Who: The Eternity Clock", available under the CC-BY-SA License.