S8·E8 Mummy on the Orient Express

Aboard the most beautiful train in history, speeding among the stars of the future, a legend is stalking the passengers. Once you see the Mummy, you have 66 seconds to live. Clara sees The Doctor at his deadliest and most ruthless - and finally she realises she's made the right decision. Because this is their last adventure: it's time to say goodbye to the Time Lord.