The BBC is to release the fourth in the Doctor Who: Adventure Games series directly after the Christmas Day special has aired on television.
The title will be available to download free from the BBC website for PC and Mac. The episode picks up directly from the third's cliffhanger.
The ‘Shadows of the Vashta Nerada', written by Doctor Who writer Phil Ford, sees the Doctor and his assistant materialise just south of London inside an aquatic sea-bed colony called Poseidon. The game features a plot which surrounds a real-world conspiracy - and takes place at Christmas.
Steven Moffat, executive producer Doctor Who said: "Shadows of the Vashta Nerada takes place entirely underwater - something which would be impossible for the TV series, as water is so expensive. It's thrilling, terrifying, educational and fun. Just steer clear of those shadows..."
The games are developed by Sumo Digital. Users outside the UK will be able to purchase and download it on the same date - details will be put on the Doctor Who website.